Twin over full futon bunk bed that supports futon mattresses is, in most ways, the same as a bunk bed for common mattresses. The only difference is that support platforms must be able to support the entire futon (regular mattresses often have internal support). These plans are for bunk beds for double size futons, but you can change to fit larger pillows by adjusting your timber dimensions.
Drill two holes into and through each end a 74-inch beam using a drill with the same diameter as your twin over full futon bunk bed. Place the holes on the center line for the 4-inch face of the beam, 3 inches and 5 inches from each end. Repeat step one for the other 74-inch beam. Drill two holes through one of your 6-inch square posts with the same drill. Drill the holes in a line perpendicular to the length of the post, 12 inches from the end of the beam. Drill a hole 3 inches from the edge of the post, the other five inches from the same edge.
Drill two additional holes in the same post lined up with the first two holes and 12 inches from the other end of the post. Repeat steps three and four to drill the other four services. Drill a hole in each of two 6 inches by 6 inch posts twin over full futon bunk bed, perpendicular to the line of the other holes. Use the same drill as for the other holes, and then drill with your drill tip to widen the holes to half an inch in diameter. Connect the rectangle with two screws in each corner, drill through the face of the 74-inch beams and into the ends of the 39-inch beams. Place a plywood board on top of the frame with the edges of the sheet at even height with the edges of the frame.