Wall Layout: We used a factory corner of a sheet of OSB as a giant framing square as we built the walls. I took the dormer's rise and run from the plans, and we cut the top plates and end studs accordingly.
Wall Layout: We laid these right-angle assemblies along the edges of the OSB to keep them square, then simply pulled the length of the bottom plates (the hypotenuse of the triangle) with a tape measure — no calculation necessary.
Studs: I laid out the wall studs working backward from the roof layout so the rafters would stack on top of the studs. The 24-inch on-center rafter layout was determined by the depth of the rake overhang — 6 inches, in this case. It pays to take time to get the stud layout right, because that generally eliminates extra cuts in the sheathing. Before nailing the studs in place, we tacked each wall triangle to the edge of the OSB "square" to ensure accuracy.
Studs: After nailing the studs in place, we added the double top plates, holding them back 3 1/2 inches to allow for the lapping top plate across the front.