A shed roof is a simple slanted type that carries water off one end. Although it's called a shed roof, it commonly is built over a deck, patio or porch and tied into the house, carrying water away from the house. Shed roofs are simple to build. Many use basic post and beam construction with rafters to hold roofing. They often are added after a deck has been built and are usually easy to attach to the existing house and roof.
Attach a 2-by-6-inch ledger board, a supporting structure, to the house wall. It should be the width of the shed roof on the deck. This is usually attached just below the eaves where the shed roof meets the pitched roof. It can be attached over flat siding, but beveled wood, metal or vinyl siding should be removed. It can be attached to the roof, but connecting joists will have to be angled to match the pitch of the roof. Fasten the ledger board with long lag bolts to strong parts of the house framing, preferably joists.
Nail joist hangers to the ledger board. If the shed roof over the deck is already built, nail extender joists from the shed roof joists to the hangers to provide a frame for additional roofing. If you are building your deck shed roof, nail joists from the hangers to joist hangers on the beam on the outside of the shed roof. Joist hangers are metal frames that nail to the ledger board or beam and have slots to hold the joists.
Tie the shed roof to the house with oriented strand board (OSB) decking. If it is a new shed roof, put OSB from the ledger board down to the end. If you are attaching a completed deck roof, measure the space between that roof and the ledger board and cover it with OSB. Nail bent metal flashing to the house wall and top of the shed roof and cover the shed roof with roofing paper and nail on shingles. If the shed roof is covered with corrugated metal, cut new metal to fit and nail it between the shed roof and the ledger board, overlapping it below the joint.