Thanks for these comments everyone. As DL alluded to I ended up with a ridge because I was designing for a shallow pitched roof (4:12) to not make an imposing structure where the space under the roof will never be used. I like the idea of the sliding rafters and would probably strap them for peace of mind. I will have plate and ridge of equal depth so it seems that the only shrinkage the will be relevant is that of the tie beam shrinking away from the bottom of the ridge post? This will result in the same scenario of the peak dropping as the ridge post settles onto the smaller tie beam, no?

DL, are you saying that the full rafter just sits on the arris of the plate? no notches? What connection would you recommend at the peak? tongue and fork, or should they just sit on the ridge and not meet each other?

Thank you Gabel for the mathematical piece of it. are you assuming something around 5% shrinkage? Also I didn't follow how you came to "13" of oak" from the example with a 8" plate and 12" ridge.

very appreciative of this forum and your time, thanks.