Decide on the size of the loft beds, considering the floor plan as well as what will go underneath and around the bed. Some loft beds are full-, queen- or king-size but most are twin-size.
Cut 2-by-6-inch lumber into pieces long enough to form a frame, slats, legs and a ladder. For a twin bed, the frame should measure around 76 by 40 inches. If you want a rail, cut a 2-by-4-inch board to the length of the bed.
Build the frame of the bed by connecting the side rails to the end rails using strong wood glue and 3-inch countersunk screws.
Cut 2-by-2-inch boards that are the same length as the inner width of the frame and glue them into place, flush with the bottom of the frame. Use clamps to ensure that the glue sets properly. Attach them using 3-inch countersunk screws placed from the outside of the frame.
Saw a piece of 4-by-8-foot plywood to fit over the 2-by-2-inch slats.
Stand up the 2-by-6-inch boards cut to the height of the bed rest the bed on top of them, with the boards in the corners of the frame.
Drill a 3/8-inch hole through the frame and legs and bolt them together using a 5-by-3/8-inch bolt and nut.
Attach 2-by-6-inch ladder rungs to one end of the bed, using 3-inch screws placed into the legs.
Sand the bed and paint or stain it to your liking.