There are two major differences between a regular bunk bed and a futon bunk bed with metal frames. The futon bunk bed will use a grid of metal tubes rather than rails to support the bed mattresses. This is because futon mattresses lack rigid internal structure and would fall through rail supports. Second, many futon bunk beds use a glider frame for the bottom bunk, meaning you can fold the bottom bunk when not in use. Although this makes the process of assembling the frame a little more complicated, it is still a simple task.
Clear the floor in the room where you want the bunk bed. Assembly will take some room, and it's easier to build the frame in place than to build it elsewhere and move it.
Identify the end pieces of the frame. Set them on the floor about as far apart as they'll be when the bed is finished. Orient them so the grooves in the bottom part of the frame face inward, toward each other.
Set the spacers in place between the end pieces. Bolt them in place with the accompanying hardware. Fasten the bolts enough only so they have a firm grip. The frame should remain loose until the end of assembly.
Lay the two panels of the couch seat on the ground. Slide one edge of the seat bottom inside the forks of the edge of the seat back. Attach them using the pins or bolts that came with the kit. If applicable, tighten these bolts all the way.
Slide the assembled couch platform between the end pieces of the frame. Position it so the sliders -- the knobs on the edges of the frame -- nestle inside the grooves.
Set the top bunk platform -- usually a single piece -- in place at the top of the frame. Bolt in place using the hardware that came with the set. Tighten these bolts all the way.
Confirm that the spacers of the bottom bunk are still in the grooves, making any adjustments as necessary. Tighten the bolts in the spacers until done.
Add the futon mattresses.
Not all futon bunk beds use a glider on the bottom bunk. For those designs, attach the bottom bunk as you did the top.