some thick grey board (cardboard)
Mess up the carpet tile a bit with soime oil pastels. The framed sign on the wall is just a frame made of grey board then painted, on top of a grubby looking handwritten sign. The mattress is two sheets of upholstery foam glued together, with some polyester wadding lumpy bits taped on, then covered with a piece of fabric. The pillow is just a miniature pillow I made. The blanket is a micro-fibre cloth. Glue everything down with the glue gun and you are finished.