Built in bunk beds with trundle bed. Gives plenty of sleeping spaces without taking up too much room. The trundle here doesn't look like it could hold a mattress and still be slid under the beds above but in general it's a great design :-)
I love this, if we ever have to have the kids share bedrooms in another house, this would be awesome! Built in, private space. Curtains could be hung. Even without bunk beds, the idea is fantastic for more than one child in a room.