Place a 16-foot 2-by-4 stud under the eaves, or "soffit," of a home. This is the overhanging part of the home where there is a gutter or water falls directly off of the shingles. Screw it to the side of the home, 6 inches below the bottom of the roof where it emerges from the wall. Use a powered screw gun and 3-inch screws. This procedure will be the same for wood or metal.
Screw I-beam hangers onto the 2-by-4 every 16 inches on center along the length of the stud for a metal roof. Use 2-by-4 hangers for wood. Hangers are small metal brackets that hold the end of a metal I-beam or stud. Use the screw gun and 1-inch screws. Hangers have their own screw holes.
Dig four holes in the ground, each 15 feet away from the side of the home. They should be directly opposite, and parallel with, the 16-foot stud. Space them 48 inches apart. Dig them 18 inches deep and 6 inches wide with the post-hole digger. Pour them half full of wet concrete. Insert a 12-foot, 4-by-4-inch beam into each hole for a wood carport. Insert a 12-foot, 4-inch metal I-beam into each hole for a metal carport. Use a 48-inch-long carpenter's level to level the posts and beams. Wait 24 hours for the concrete to harden.
Screw a 16-foot, 2-by-4 stud to the inside at the tops of the posts for a wood carport. Place it flat against the sides of the posts. Make the top edge flush with the top of the posts. It should be directly opposite and parallel with the stud that you screwed to the side of the house -- but lower depending on how high your eaves are. For metal, bolt a 16-foot metal I-beam to the sides of the metal posts. There are holes in the beam and the post for this purpose. Use 1/2-inch bolts provided with the metal parts for this purpose. Use a 1/2-inch socket and ratchet.
Screw stud hangers 16 inches apart, directly opposite the hangers that you screwed to the stud on the wall for a wood carport. For metal, use metal hangers and bolts.
Measure the distance between the hangers. Cut a 2-by-4 stud for each pair of hangers for a roof joist. For metal, measure the distance and order the metal joists. Drop the studs into the stud hangers and screw them in. Drop the metal joists into the hangers and bolt them in.
Place 5/8-by-48-by-96-inch sheets of CDX plywood on top of the joists for a wood carport. Cut and fit them to overhang on the outside edge of the joists by 6 inches on the outside perimeter of the carport. Screw them to the plywood with 1 1/2-inch wood screws and the screw gun.
Place composite asphalt shingles over the top of the plywood to cover. Staple them in place with a roofing staple gun to complete a wood carport design.
Place corrugated metal roofing on top of the roof joists. The pieces should be 16 inches wide and 18 feet long. They bolt to the tops of the joists, side by side. Each piece should overlap the previous piece by 1 1/2-inches. Use a cordless drill to drill bolt holes where needed.