The main difference between a bed standard bunk bed and a futon bunk bed is mattresses. Regular mattresses have an internal frame, which means they do not sag. Without an internal frame, a futon mattress case comes through the rail and must be supported by a grid or a set of bars. Although different brands and models of futon bunk bed big lots have different mounting details, most follow the same general plan. The construction will be much easier if you have a partner to keep the frame steady while you work.
Set the pieces for your bed futon bunk bed in your work area. Place all nuts and screws that came with the bed in a plastic bowl. Place the end pieces in the bunk bed frame in place, approximately where they will be when the bed is finished. Leave at least 12 inches between all edges of the frame and walls so you can move around while working. Mount the bottom mattress frame. Place it in place and attach it with four or eight bolts, depending on the model. Slide the bolts in with the heads pointing outwards. Screw the matching nuts on about three quarters of the way.
Mount the upper mattress frame, using the same method as the lower frame. Tighten all nuts on both frames by hand until you can no longer move the nuts. Tighten the nuts further by holding the nut in place with a wrench or locking rods, and then screw the nut in place with a screwdriver or Allen key. Attach any guardrails that came with the futon bunk bed. Bolt them in place using the same basic technique you used to attach mattress frames.