When I first moved to Georgia Tech, I was living in a very small 1BR/1BA apartment. After being there for a while, I decided to make a bed that could fold completely out of the way. It is totally freestanding and holds a queen sized mattress. It takes a little bit of strength to lift up, but not much.
All of the design work can be found on GrabCad. Do note that I did make some minor design changes as I went during fabrication and never did put those back into the models.