I am doing this with Little P's room. The higher one is going to be his clothes and the lower one will be toys and books. They aren't going to be that high (The clothes will be a little higher so he can't reach them)
This is the perfect place to put a pull out bed! I always look at those beds and thing they're impractical because it's too hard to leave all of the open floorspace needed for one but I'd happily do it for this library/reading space.