Divide the floor into an 8 X 8 grid. Arrange piles of laundry, books, pizza boxes, etc. on the grid and tell your roommate that you've turned the room into a chess game and not to move any of the piles.
Here is a classic which has been fading into a lost art. It works extremely
well someplace like a military academy or such, where everything must always
be in impeccable order, but can be used for good effect in a dorm room, too...