Most simple bunk beds are designed from standard, twin-over, L-shape, loft and triple-loft shapes. The choice between them largely depends on the dimensions of the room and the number of people who sleep there.
The standard bunk bed is simply a bed stacked above another in parallel formation, and both bunks' mattresses are the same size. This is slightly different than a twin-over design, in which the bottom bunk is generally a full-sized mattress and the top is a twin. The L-shape design has the bottom bunk arranged perpendicularly to the top one, rather than parallel. The loft bunk is simply a raised bed that creates more floor space underneath to maximize the utility of a smaller room. Finally, a triple-loft bed is an arrangement of three stacked bunks.
Bunk beds are a means to more effectively use vertical space, so it is common to see variations within these types. For example, a standard bunk or a triple-loft can be built right into a wall.
Lofts are very versatile, and the space beneath can be used for a desk, a dresser, a futon or a trundle bed. Even a full-sized bed can occupy this space to create an unattached twin-over. An L-shape offers an alcove area beneath the upper bunk; this is much like a loft bunk, but with less disposable space.