Bunk bed cubbies: could build a box for the bunk beds, curtain over each cubby. (leave out the TV that is in the bed in the picture- kids do not need to watch TV in bed). Could build something similar for a reading nook instead of sleeping area.
Who doesn't like a cozy little nook to sleep in? This design makes great use of the space allowing enough room for 4 people to sleep, each with their own private quarter. Great idea for a guest house or cottage bedroom.