Installing the new roof.
Framing a new roof over an old roof.
Your second row of shingles should be cut to 10 inches wide.
A new level 2 6 ridgeboard and rafters then are assembled over the old roof and are attached to the existing structure with nails and lag screws driven into the underlying wall top plates.
Use 1 5 or 1 75 inch roofing nails.
Closed cell polyurethane foam insulation is sprayed around the new roof frame sealing edges and providing support for the rafters and the ridgeboard.
To provide a framework for the new trusses nail 2 by 6 inch strips of wood around the perimeter of the roof.
Or if you want to raise the roof a bit more install fascia around the roof perimeter attached to the new soffit and nail the new roof deck to crown molding above the fascia.