My older two boys share a room and sleep in bunk beds. Since we moved them to bunk beds it's been great as it has opened up a ton of space in their room for quiet time away from the chaos of the rest of the house. I love bunk beds.
This is another example of a layout that would be easy to install in a studio apartment - a loft bed with stairs would be a cheaper and nicer space saving solution than buying a Murphy bed. Maybe even in a small bedroom.