Get the materials for the frame at your local home-improvement stores. Scrap wood can be cut to size. Construct the platform frame with four wooden planks (three 2 feet by 2 feet and two 2 feet by 4 feet). Use four wooden posts (4 inches by 4 inches) as legs, cut to the desired length to determine the height of the platform. Sturdy strips of wood (2 feet long) provide support for the mattress.
The materials for the mattress can be obtained from any craft or fabric stores. Adjust the thickness and firmness of the futon mattress with sheets of foam Cotton batting will provide an outer layer for comfort. Pillows can be placed on top of the foam sheets for additional comfort. The mattress pad can be further customized by choosing fabric such as canvas for durability or fleece for softness.
Drill holes into the wooden planks approximately 1 inch from each end. Drill holes 1 inch from the top of each post on two adjacent sides. Assemble the rectangular frame using two short and two long planks, and nail the corners in place. Align the drill holes at the corners with the holes on the legs. Fasten the legs into place using washers, nuts and bolts. Repeat on all four corners.
Insert the remaining short plank in the center of the rectangle and screw it in place. Nail the strips of wood at regular intervals on each side of the center support ideally 2 inches apart. The strips of wood provide support and ventilation for the mattress.
Measure several thick sheets of foam to 1.75 feet by 3.75 feet. Stack the sheets to the desired thickness and roll several layers of cotton batting around the stack to create a soft surface. Cover the soft foam stack with material, and sew the back and sides closed. Place the mattress on the wooden slats of the platform.