Thanks Carl,
Not sure how far along you are but have you considered a ridge beam and common rafter design? The ridge beam being simply a third plate with which to rest the top end of the rafters on. Just birds mouth both top and bottom ends of the rafters and lag them down. No notches are required in the plates as the outward thrust has been eliminated by the ridge beam. As for bracing, just brace as if it were a wall from the plate to the king post which sits atop of the tie beams.
Also, there is a Simple Beam Calculator which has been seen a few time on this forum and is very handy for these simple structures. I can send it to you if you don't already have it.
Thane
