A small space idea, like a tree house in your room. Utilize all space with shelf stairs up to the bed box. Get a closet too and all of it up off the floor space. Great for a boys room. Put a BB Net on the bed and voila! they can play indoors.
Levitate Architects used a staircase to a loft-like bedroom to create an enormous amount of book storage space. Even though the staircase isn't very compact but could accomodate so many books that it would save some space anyway.
basement stair cabinets, stairs with flip up steps and very narrow stairs. Each step goes up one at a time for each foot. It is sort of spaced so you are putting one foot per step with a steeper step. Very space-saving.