Measure the desired door, then mark off an area of the wall the same size as the door. Extend these marks slightly, keeping the frame in mind. Remove the interior wall, insulation and any electrical wiring. Install the patio door frame, then use a circular saw, hammer and chisel to remove the exterior wall. Adjust the frame and door so it sits square and plumb in the rough opening. Screw in the hinges, install the door, and seal any cracks.
While installing the patio door, make sure all cuts in the wall and any structures added are even, level, and square and plumb to the existing wall. To seal the patio door, use building paper, silicon caulk and drip edge. These materials help insulate the door and keep moisture, dirt and debris from entering through the patio door.
A threshold also keeps the elements out of the home. Install one by measuring the space between the door and the floor. Cut a piece of wood, metal or plastic as wide and as long as the door to this height. Using a drill, screw down this piece of material, and install shims under each screw hole to keep the screws from pulling the threshold out of shape. Use a handsaw to trim away any excess shim. After installing the patio door, fill any nail holes, and finish the door to protect it from damage. Repair any damage to the interior wall or exterior siding, then install and finish the interior door casing.