Thanks, Gabel. I have been playing with Plumb Line Scribe on a small project, and I am now going to add a ridge to it for the reason you pointed out. I had been wondering how the rafter peaks were going to scribe in and this answers the question in the back of my mind. So both the plate and the ridge are set to the lines on the floor and scribed, accommodating both sides with the same lines, too.

I just hold the ridge up with an additional gin pole while the rafters are poked in place. So assembling is a breeze.