"Consider doing bunk beds built into a closet in a room, that way you don't loose square footage. Otherwise consider doing bunk beds such as these but have 4nin the room. This will allow for a higher rental price"- www.thisheathyhouse.com
This room in my cabin with a little more floor space but...."WOW! Enough room for a family of 6! 2 sets of bunk beds + 1 double bed fit every one into the small sleeping room. The closet was removed to gain room and storage is in baskets that slide under the beds." A good mini guest room...I'm totally doing this when the kids move out.