If I could design my own room it would contain a king size bunk-bed, a flat screen TV, a trapdoor that would go into a underground tunnel that would have a room made out of Lego bricks, a room that is a bouncy house, and room that is made of mirrors. It would have a rope ladder that goes to an ultimate, huge, and awesome play scape on the roof. It would also have a huge hot tub, a huge pool, and a huge sauna. It would also have a closet that was really cold and would be good for storing food (and it would be good when I am hot).
The floors, walls, and ceiling would be made of iron. I would have lockers that had either metal armor or metal weapons in them. I would have a big couch. I would also have a huge desktop computer.
Sounds like a pretty awesome room. A definite fun place to hang out.