Footings & Posts
Generally, build 8 x 8 or 12 x 12 inch wide footings for 4 x 4 posts. Construct 16 x 16 inch wide diameter footings for 6 x 6 posts. Make each footing 8 inches thick. Dig a hole below the frost line in your area. Pack the soil at the bottom of the holes. Build the forms out of 2 x 8 boards. Use ready-mix concrete and insert two reinforcing rods in the first 2 inches of concrete and in the last 2 inches of the concrete at the top of the footings.
Cross the rods in an "x" position. Insert anchor bolts into the center of the wet concrete and place 4- or 6-inch wide galvanized steel post bases slight into the wet concrete. Pack gravel around the footings and the posts. Encase the posts in gravel up to the soil surface. Keep in mind that the posts will also support the cross beam for the shed style roof.
Joists & Deck
Join the porch deck to the house with a ledge board, which should be placed 3 or 4 inches below the door. Install metal flashing between the house and siding and over the ledger board, to prevent water penetration between the house and the deck. Make sure that you use fasteners that meet the local code requirements. Typically, lag screws or 16d gauge nails may be used to do the job.
Install 2 x 8 band joists around the perimeter. You can strengthen the structure by doubling these joists. Use metal joist brackets to secure the floor joists to the ledger board and to the band joist opposite the ledger board. Allow a slope of 1/4 inch per foot for the joists, which will to allow for proper drainage. Install five 4 x 6 deck boards and secure them with deck screws.
Railings & Stairs
Most codes required railings to be 36 inches high. Attach 4 x 4 posts to the deck and the band joist just below the deck. Use 2 x 4s for the top and bottom rails. Attach the pickets between the rails. Make the stairs a minimum of 3 feet wide. Purchase a set of stringers or build your own out of 2 x 12 lumber. Use the same board installed on the deck for the treads.
For most single-story homes, secure the ledger board under the edge of the roof. Otherwise, fasten the ledger board into the studs of the wall. Secure a beam, made out of 2 x 12 boards, on top of the posts. Secure 2 x 8 rafters, 24 inches on center, to the ledger and rest them on top of the beam. Install 5/8-inch plywood perpendicular to the rafters. Cover the roof with a felt underlayment and shingles or material to match the house roof.