Cut angle metal into three 36-inch pieces, 10 12-inch sections, four 24-inch strips, four six-inch sections and four three-inch pieces.
Attach two 36-inch pieces and the six-inch sections to the underside of the plywood for support and frame mounts. Using stove bolts and washers, mount the three-foot sections parallel to each other, eight inches and 26 inches from one of the four-foot sides of the plywood. Place two three-inch pieces perpendicular to the long sections at each end.
Set two 24-inch metal pieces on the ground three feet apart, facing each other. Place the remaining six-inch section perpendicular to and directly above the two 24-inch sections on the ground. Insert an upright 12-inch piece at the corner of the 36-inch piece and one 24-inch section and connect with hex bolts and wing nuts. Repeat with the other 24-inch strip.
Attach four 12-inch sections at angles to brace both sides the vertical supports by creating triangular frames at the the ramp's base.
Place the plywood board on the ramp frame so the metal connectors align with the frame supports; hold in place using bolts and wing nuts.
Use the remaining metal strips as interchangeable parts to adjust the height of the ramp for the desired purpose. Remove bolts and nuts for adjustment, to disassemble and store.