Use your screwdriver to remove the bottom hinge from two sets of bi-fold doors, and remove all the hinges from a third set. Open all the doors and lay them on a flat work surface so they are side by side. Use your screw gun to attach each of the five doors together. Alternate the direction of each hinge so all the doors form one solid structure. Do not install any hinges below the center point of the doors. The lower end of the doors must remain free from hardware to allow for cutting in the next step.
Use your straight edge and pencil to mark a line across the doors just above their bottom panels. You will using these bottom panels to build your footboard. Use your circular saw to cut across your pencil line.
Turn the five bottom panels sideways, and line them up side by side without any gaps between them. Measure the full length of the panels from end to end. Use your circular saw to cut a piece of 1-by-3 inch stud to the same length. Lay the 1-by-3 across the five panels at the bottom, inside edge, and fasten it in place using your screw gun and 1 1/2 inch wood screws.
Cut a second 1-by-3 inch piece of lumber to a length about 1 1/2 inches longer than the the first. This extra length will provide a 3/4 inch overhang on each side. Smooth over the edges of your 1-by-3, and remove any rough spots with your sander. Spread a bead of wood glue along the top of your footboard, and fasten the 1-by-3 in place using your hammer and finishing nails. Check that the overhang is even on both sides, and at both ends before making the installation permanent.
Measure the height of your bed, and determine the appropriate height for your footboard. Use your table saw to cut feet from a 2-by-4 inch stud. The feet should be equal in thickness to the footboard, and as wide as you deem aesthetically pleasing. Use your drill to bore a screw hole most of the way through the leg, from the bottom upward.
Drill a pilot hole in the bottom of the footboard at each corner. Use your screw gun to drive 2 inch wood screws upward from the bottom of the feet, and into the footboard.
Sand and paint, or stain your footboard as desired. Stains can be selected to match existing furniture. If you prefer paint, first use your paint brush to coat the footboard with primer, then apply two coats of the semi-gloss paint of your choosing.
Reverse your metal bed frame so that the large corner brackets which normally rest at the head of the bed are now at the foot. Stand your footboard along the bottom of your bed, so that the feet straddle the outsides of your metal frame. Use your screw gun, 1 1/2 inch wood screws, and washers to fasten the footboard to the frame. Drive screws into the footboard legs from the inside of the metal brackets until the footboard is firmly attached.