Choose a wagon chassis from a farm equipment dealer.
Measure the distance between the bolsters; i.e., the long vertical bars on the sides of the chassis. This measurement is the length of the wagon deck.
Cut enough 4-inch-by-8-inch boards to the length measured plus 4 feet. These boards are called stringers.
Drill 1/2-inch holes into each end of the stringers. Use these holes to attach the stringers to the chassis with bolts.
Measure the length of the base. Determine how many cross boards are needed by measuring for perpendicular placement against the stringers. The cross boards are 4 inches by 4 inches and must be spaced 4 feet apart. Use the circular saw to cut the appropriate number of cross boards and attach them to the specific places with 1/2-inch-by-12-inch bolts.
Use the measured length of the wagon frame to determine the number of 1-inch-by-12-inch planks needed for the deck. Divide the length by 12 and cut that many boards to the width of the deck. Lay the planks across the cross boards without attaching them to the boards.
Build two clamps by bending four metal straps, using a bench vise and a heavy hammer, to the width of the top edge of a deck board. Drill a 1/2-inch hole in the metal strip on the end away from the bend.
Place the clamps on the end boards of the deck. Run a threaded rod 1/2 inch in diameter through the holes in the clamps and screw a nut on each end of the rod.
Tighten one end of each clamp rod until the planks are closely fit together. Lay a piece of angle iron over the planks above the cross boards. Drill the outside planks to the cross boards through the angle iron with 1/2-inch-by-6-inch bolts. Screw nuts onto the bolts and tighten them with the air drill.
Drill 1/2-inch-by-14-inch bolts through the deck planks, cross boards and stringers and secure with nuts and the air drill at 4-foot intervals. This completes the deck of the wagon.