An Interior Designer Is You

"Iolo: "Are we using the transdimensional legacy of a long-dead civilization to store all our stolen goods in a place where they can't be stolen back?" Steve The Avatar: "Mmmmmmmmaybe?""

- Let's Play of Ultima VII: Serpent Isle

So, you're playing a videogame, and you have your Player Headquarters. It could be a house. It could be a military base of some kind. And, you know, it's a nice place. Well, OK, the walls are kinda brown and boring. And except for the conference table, it's kinda empty. And maybe the carpet could use some scruOHMYGOD! This room needs a makeover STAT!

Luckily, this isn't hard. Why? Because An Interior Designer Is You!

In some games, you'll get a room (or two, or three) that you can kit out as you see fit. You can collect furniture and other decorations, put them up in as weird a combination as you please, and just generally customize your space. Sometimes, you only have a few different decoration options, and you can only change the "style" of items. Other games give you complete freedom to place items.

Compare Virtual Paper Doll, An Entrepreneur Is You.

Action Adventure

 * Castlevania: Harmony of Dissonance had a room which you could decorate. It didn't fit with the rest of the game very well (and doesn't make sense character wise, Juste, as a Belmont, is in a position to know the castle will disappear/fall apart when he's done) . It's a borderline example, though -- you couldn't choose the placement of the items.
 * Castlevania: Curse of Darkness is the next in line for this, except that you only have chairs to decorate your room.
 * Overlord offered a limited version of this with your tower, once you had upgraded or bought an item that was pretty much it with only the flags capable of switching.
 * The sequel expands it to give you a choice of three different styles for each item.
 * Indie Metroidvania An Untitled Story lets you decorate a personal room by purchasing furniture. Although they're placed in preset places, you can buy quite a lot of items including arcade minigames which are necessary for full completion.
 * Joe & Mac 2. You can buy furniture for your house.

Adventure Game

 * The Quest for Glory II remake gives you your own room in the inn. As the game progresses, you can buy decorations from various shopkeepers (potted plants, wallhangings, trashcans, etc) and place them in the room to make it more like home.

Fighting Game

 * Smackdown vs Raw 2007 enabled you to customize and explore the locker room. Interior designer indeed.
 * You can also do this in 2006, but you can't freely walk around your locker room like in 2007, just move around to get to all the different options easily.
 * In WWE '12, you can customize your arena to your heart's content.

4X

 * You could customize your palace in Civilization, and improve your throne room in Civilization II (though in the latter, you had no choice of style).
 * Civilization III has this as well, if you hit a certain objective. You could choose styles, but it's basically just designing the same thing, in the architectural styles of different civilizations, making this more of "An Architect Is You".

MMORPGs

 * City of Heroes lets you decorate your Supergroup base as you see fit, with both functional and purely decorative items. This may end up costing a lot, especially for solo and small group attempts.
 * In EVE Online, you (or your corporation, which is pretty much a clan) have the ability to buy and anchor a player-owned starbase, abbreviated POS, starting with a control tower. You can then add on modules such as turrets, auxiliary power arrays, shipyards, refineries, or moon miners, as well as other things.
 * If your alliance claims sovereignty over a solar system, they can put their efforts together to produce an immensely expensive and useful Outpost -essentially a player-built space station. Just be prepared to defended, because hostiles can attack and take over your hard-earned station.
 * Final Fantasy XI lets you do whatever you want with your Mog Room House. The furniture also gives a special enhancement for you. Oddly enough, you could customize as much as you want, but you couldn't let anyone in for years until a patch was made. Furnishings became even more popular after the Storage system (a free room for gear from furniture) was drastically improved, allowing 80 Storage without causing your Mog Safe to have a heart attack. No sane Adventurer would go without a snazzy living space.
 * Gaia Online's house feature has several models, an expansion option, and a furniture store with Ridiculously-Human Robots as attendants.
 * The Allegedly Free Game Glorified Chat Room Habbo Hotel, where to get even a single credit you had to spend real money, and you don't get any furniture to start with.
 * Newbies do get some starter furniture there now. One piece per day throughout a week, but you get the idea.
 * The MMO version of Monster Hunter lets you do this. As per series tradition, most of the furniture is made from monster bits (hide, shell, scale, etc).
 * Neopets has "Neohomes," which you can fill up with furniture. The furniture is quite small compared with the rooms.
 * Emphasis on was. They've made "Neohomes v2" which are isometric, and everything is now carefully scaled... if it was lucky enough to be upgraded for v2 compatibility.
 * Petpet Park also has this now.
 * Pangya has recently added a "My Room" feature with furniture and decorations and such... which serves absolutely no purpose whatsoever since you are the ONLY one who can even SEE it.
 * Phantasy Star Universe provides players with the ability to decorate their rooms with all sorts of rare trophies, common dolls, and various seasonal kinck-knacks. Players can also choose the basic theme (up to and including the perceived planet for their home) as well as what music plays in their room. This all serves a real purpose as players go to each other's rooms to buy stuff. There is even a Gachapon decoration which allows players to vend items to each other in sort of a gambling mini-game.
 * Playstation Home is all about this.
 * Among the things you could buy and/or win in Puzzle Pirates is furniture, with which you could decorate your home or your ship if you so desire.
 * Runescape added construction quite a while back, which requires a whole lot of resources, and is a major Money Sink.
 * Runes of Magic uses free (and, for all intents and purposes, immediately available) player housing as a marketing bullet point. Decorations can cost a lot of money, but some of them have practical uses.
 * Second Life
 * Travian gives you a small house to start with, which you can upgrade into bigger and bigger houses as you gain the currency to do so. Each house has a set of rooms you can decorate with wallpaper, furniture, and even plants and streams for the backyard. What's even cooler is that they use contests to solicit player designs, so some of the larger house blueprints and some of the furniture collections were actually player-crafted.
 * In Virtual Magic Kingdom, the otherwise lackluster MMORPG based on the Disney Theme Parks, had a pretty nifty room-decorating feature. The rooms, furniture, and accessories were themed in accordance with various park attractions, and you could use "teleporters" to link up different rooms. Eventually, they added a feature where you could actually buy sections of ride track and set up rides in your rooms.
 * Webkinz
 * The Lord of the Rings Online lets you decorate your house with trophies from your many kills. Nothing says cosy hobbit hole like a dragon's head on the front lawn, and a barrel full of tentacles in the bedroom.
 * EverQuest 2 offers housing suitable for a wide range of budgets, and certain tradeskills allow players to make furniture and decorations. And that's not even getting into the sheer number of quest rewards that can be used to spruce up your quarters. The Lore and Legend quests are all over this: research a particular type of creature, and you're rewarded with a trophy weapon to stick on your wall, and a placeable (and readable) book on the subject.
 * Club Penguin lets you, if you're a member, decorate your igloo with items you buy from the catalog, and you may also upgrade it to things such as a bigger split leveled igloo, snow igloos, candy igloos, backyard igloo(s), a halved igloo, stone igloos, a cozy cottage and some weirder stuff, such as a gingerbread house, a fish bowl, a gym and an estate igloo. Of course, there are loads of furniture to choose from, though a lot of it has been clearanced from the catalog. Oh, and let's not forget that feature which lets you put various flooring in it, such as various wall-to-wall carpets, bamboo flooring, phony-lawn, snow, tiles, cobblestone and even a disco floor. Which is quite laggy when you've got loads of random furniture shattered around your igloo. Especially when the aforementioned furniture is animated. Lag, lag, lag...
 * Wizard 101 lets you decorate your dorm room with furniture you get from quests and the like.
 * A majority of virtual worlds have this nowadays. Toon Town, Pixie Hollow, Fantage, just to mention a few...
 * Dragon Quest X.

Platform Game

 * Kirbys Epic Yarn lets you furnish Kirby's apartment with items found in different levels, or purchased from shops.
 * Little Big Planet does this of course, not only by a level editor, but by being able to decorate your pod.

Puzzle Game

 * Professor Layton and the Curious Village: As you progress through the game, you can collect items to furnish Layton and Luke's rooms at the inn. Finding the best combinations of items to max out their happiness levels unlocks extra puzzles.

Real Time Strategy

 * In Age of Empires III, you can buy purely cosmetic items for your home city to characterize it. This ranges from patriotic bunting for the buildings to have a town drunk staggering around the dock.
 * Almost every quest in Little Kings Story gives you new pictures to hang around the halls of your castle.
 * In RHDE, each player can buy furniture from the shop and place it in his house. Rounds are won and lost by how much furniture is in your house and how it is arranged.

Rhythm Game

 * Hatsune Miku -Project DIVA- has a "Miku's Room" feature, which lets you decorate Miku's room with items unlocked through the game. You can also watch Miku interact (mildly) with the stuff and take snapshots of it. This is continued in the sequel with the DIVA Rooms, where each Vocaloid in the game has a separate room.
 * Lego Rock Band allows you to decorate your band's den with various knick-knacks.

Roguelike

 * Dwarf Fortress, where the decorations range from "rock statues" to "iron thrones" to "hapless goblins that blundered into a cage trap for your dwarves to poke with a stick". Many items have an in-game purpose, but others simply provide a morale boost to the inhabitants of your settlement as well as looking damn cool. It's also possible to order sections of wall and floor engraved for a similar effect, and there are medium to long-term plans to enable the player to commission an individual statue or engraving of something.

Role Playing Game

 * Justified (and part of the gameplay mechanics) in Dark Cloud - parts of the world have been sealed away to protect it from a malevolent genie, and It's Up to You to find all of these bits of world and reassemble them.
 * In the first Deception, you can add rooms onto your castle. Most rooms are purely cosmetic, but special strategic rooms exist as well which grant you some additional features.
 * It was possible to do this in The Elder Scrolls IV: Oblivion. It was just insanely hard; the physics engine made it difficult to make that one perfect placement for your pretty vase on the narrow table. There are tons of GameMods out there to fix just that problem.
 * This also leads to a case of Mundane Utility, as Telekinesis spells (Mysticism school) are very useful in interior decoration. Still don't expect to place more than 3 books on a shelf.
 * As far as can be made apparent through hacking, Bethesda was attempting to implement furniture purchasing in Daggerfall to complement the house you could buy, but never got around to either completing it or implementing it. It didn't help that their container system was buggy and that all items looked like miscellaneous treasure piles out of the inventory.
 * Oblivion has many instances where this was done by modders. Judging by the internals of most add-on player houses, one would think many modders are architects and decorators when not playing games.
 * And some of your houses, when fully outfitted (Cheydinhal, Skingrad), count as Scenery Porn in their own right.
 * In The Elder Scrolls III: Morrowind, all inventory objects could be placed around the map, giving a treasure room effect. Chairs and other furniture, however, were static. Most of the world was made of bottles.
 * Skyrim continues the tradition, with the welcome addition of bookshelves-as-chests that automatically arrange dozens of books on their shelves.
 * You can buy houses in Fable. You can't customize them much, but you can increase the quality of the furniture and hang trophies on the walls.
 * Fable II allows a bit more customization, with the ability to buy furniture and use it to replace the furniture a house came with (though only the same kind of item in the same place).
 * Fable III allows a choice of furniture in various places, placement and choice of carpets, and choice of wallpaper. You can also have John Cleese arrange the furniture for you.
 * In Fallout 3 you can purchase decoration themes for your house as well as useful upgrades such as a workbench, lab table, and a soda machine (It makes your soda cold, improving its HP restoration ability). And any clutter (Old books, dinner plates, teddy bears, etc) you can pick up around the game world can be placed in your house.
 * Trying to do the last thing can cause much frustration thanks to a rather wonky physics engine.
 * At least one mod allows you to build a settlement from the ground up, decorating it with whatever you want and populating it with people you recruit. So it's really this, but on steroids.
 * Legend of Legaia 2 had this as one of its minigames: you had to redecorate the main heroine's room with various items you can find around the world, with some of them only gotten from an auction or a vending machine, or in other words, a Luck-Based Mission. The reward for finding all the items and decorating the room in one very specific way was an ultimate crafting material for both of them though.
 * Pokémon Gold and Silver/Crystal let you decorate your room. While you had relatively limited options as to where you could place things, a decent number of collectibles were available.
 * If you let your mom keep half your money, she will occasionally use it to buy an item for your room.
 * Pokémon Ruby and Sapphire/Emerald let you not only decorate your room (with dolls), but also a "Secret Base" in a tree, cave, or bush, which you could fill with tables, chairs, mats, toys, plants, and other various decorative items. If you "mixed records" with friends, you could also visit their bases and battle them.
 * In Pokémon Diamond and Pearl/Platinum, you still have a Secret Base--but now it's underground, and there are more furniture options. Bases are also now used for a Capture the Flag mini-game.
 * Platinum added a Resort House with different furniture from the bases. Your in-game friends occasionally come visit you there.
 * In HeartGold/SoulSilver, they took out the room decoration as featured in the original game, and instead allow you to customize the Safari Zone by putting items in it to your liking. Some of the items summon or increase the odds of finding certain Pokémon; other items are purely decorative.
 * In Pokémon Black and White, the Dream World allows you to decorate your Pokémon's home with various furniture.
 * In Skies of Arcadia you can customize your entire base with either a Western or Eastern feel, including fountains and what kind of food is served in the mess hall.
 * The first Suikoden game let you customize a few areas of your castle, mainly the bathroom. Later games follow this trend -- you can hang paintings and wall scrolls, place statues, plants and pottery, all in the designated areas...
 * In Suikoden IV, the player even recruits Penelo, an interior designer who promptly takes over a room on your Nice Boat and lets you spruce it up with furniture, wallpaper and carpet... and putting together a full set nets you special comments from certain characters.
 * In the SNES RPG Terranigma, you can buy a house and kit it out with increasingly fancy furniture. This serves no useful purpose to the game, except that you can sleep in the bed (which worked as a free inn).
 * The Way Chapter 6 lets you purchase a house and fill it with furniture.
 * In White Knight Chronicles the player can customise their own Georama essentially acting as their avatar's hometown for the online aspect of the game though it can also be viewed and visited offline as well.
 * Recettear: You can customize your shop. It's justified in that the decorations attract different customers.
 * In Mass Effect 2 Shepard can customize his/her quarters with souvenirs from various shops - ie: fish (that you could feed), a hamster, model starships - as well as various trinkets found during subquests (a Prothean relic, Shepard's old N7 helmet, etc.)
 * You could do this in some of the Ultima games, most notably Ultima VI and Ultima VII. The page quote is from Ultima VII Part Two, and is about an extra-dimensional transport hub accessible via the Serpent's Jawbone. The player went through the area often, so it made sense to set up headquarters there.
 * In Ultima VI, you could use pretty much any house near where a red moongate would drop you off. Killing the home's occupant was optional - however the beds in the game are unusable items by the PC so if your party wanted to sleep to get health back you had to go into the wilderness or use an Inn.
 * Dragon Fable allows you to purchase and decorate a house, even customizing it down to the point of choosing the setting and house style, but there isn't too much houses can do for you unless you shell out money for in-game special currency (or get lucky with item drops). If you do have enough Dragon Coins, however, you can have a lot of useful items, such as easy access to almost all armors/classes, a convenient way to save your default weapons/armor, and even a little practice arena to farm in.

Simulation Game

 * Pretty much, oh, most of the reason for Animal Crossing's existence. The majority of the game revolves around collecting and placing furniture. And even non-furniture items can be used to decorate your house. And don't forget you can even design your own clothes, wallpapers, and floorings, AND MORE!
 * Elements of this can be found in Evil Genius, where you play a campy 1960s Bond villain. It's something of a sandbox game, so you get to build your evil fortress and stock it with necessary items, traps, and trophies you've stolen from around the globe. Put some of your ill-gotten gains near your minions to keep their morale up, and put the rest in your private Inner Sanctum.
 * Harvest Moon DS Cute allowed you to buy different wallpaper and carpet themes for your house, as well as offering a few different kinds of furniture. Most of it, like the kitchen and the big bed, was necessary if you wanted to get married, but others, like the bear "Dachan" and the vase, were optional.
 * Animal March gives you outright control over the layout of your house, with lots of optional furniture.
 * Seeing as it's Animal Crossing, the Konami game Magician's Quest: Mysterious Times also allows you to decorate your dorm room.
 * This is pretty much the entire point of The Sims (indeed, it was originally meant as an architect simulation) as well as MySims and MySims Kingdom. The last of these even gives you.
 * Sim City lets you do this with a city.
 * And SimEarth lets you do it with a planet. Raise the land in funny shapes, artistically bombard a continent with meteors, or why not tamper a little with the ozone layer and start a new ice age for that art deco "huge walls of ice crushing all life" feel to the place?
 * And Spore lets you do this with - AN ENTIRE GALAXY! But not plants.
 * You can access the plant editor which is buried deep inside the game with a little bit of code inputting.
 * Space Colony lets you play interior design in your colony. Interestingly, things like noise pollution are taken into account.
 * Pretty much every Facebook business management game, including Farm Town, its clone FarmVille, Island Paradise, Restaurant City, Hotel City, Cafe World, etc. is essentially test grounds for wannabe interior designers. These games include the ability to decorate one's farm (or whatever) with items of various prices. Restaurant City has it so bad that the game designers implemented several "layouts", so people can display all the cute furniture and decorations they had bought, and rotate them.

Stealth Based Game

 * In Assassin's Creed II, your Monteriggioni town and villa could be upgraded to give you a massive income and discounts.
 * And in Assassin's Creed Brotherhood, a City Planner Focused On Urban Renewal Is You, as you can now do this for the entire city of Rome.

Wide Open Sandbox

 * Little Big Planet lets you customise your Pod, which functions as the main menu in the game.
 * Saint's Row 2 allows the player to purchase about a half-dozen "cribs" in various places and upgrade to a limited selection of new furniture. Also, the gang's headquarters is renovated automatically as missions are completed.
 * Scarface the World Is Yours has a 'Pimp Your Mansion' mode. While actually placing the things you've bought is unnecessary and unrewarded, buying ostentatious and expensive junk is more or less essential to increase your respect level.
 * Unfortunately, in some versions of the game, placing your kitsch can become buggy, with pieces disappearing from where you place them after leaving the mansion. However, there are a few different decor selections that alter the mansion's overall look, from the classic '80s movie style, to a tastefully modern style complete with shark tank, all the way to a quasi-Roman villa.
 * Arguably the whole point of Minecraft, except with, well, mines. (And, eh, crafting.) Taken a step further with dyes that let you color wool blocks or even sheep, which also drops wool blocks of the dyed color once you shear them.
 * Pretty much any place anywhere can be decorated to your liking. Want to build a base inside a cave? Go for it. Want to make a house entirely out of dirt and sand while the inside of it is made out of bricks? It's possible. Do you want to fill your basement with a pool of lava? Go nuts! It's also possible to build structures and the like in the Nether (a place mostly made out of fire and lava) an in The End (an alien world pretty much). Creative mode gives you access to every single block and item, allowing you to literally make anything you can think of.
 * Terraria actually requires you to decorate your house with reasonably sized rooms that contain at least a chair and table in order for helpful NPCs (who sell you equipment) to move in. In general the game gives you a lot of freedom for decoration, but most items have an ingame purpose as well as just looking nice.

Software

 * Any and all room planner software, anywhere, ever. You start out just trying to rearrange the apartment, but you just give up and just started making 1 Awesome Drive.