I recently added three dormers on a 12:12 roof, using a toe-board and roof-stair system that saved me a lot of time, risk and effort. As shown in the drawing, the stairs are made of two 2×12 stringers with 16-in. long, 3/4-in. plywood treads. The uphill end of each stringer was cut in a curved pattern to keep the front edge from damaging the shingles when it slid onto the roof. The downhill end should be notched on the underside for a flat 2×4 toeboard. I placed one ladder on each side of the dormer layout, and hooked them over the 2×4 toe board that was nailed at the eave parallel to the ridge. A 2×12 plank could then be laid across the treads of the two stairs, and moved up and down the pitch of the roof. Framing, siding, trimming, painting and shingling the dormers and surrounding area were relatively easy, and the system caused a minimum of damage to the existing roof.
Wayde Millany, Dillon, CO