As the guys were installing the zinc roofing, we had most if not all of the gap-oh-sis taken care of as far as the flat sheets. Where we had a question was with the roof ridge cap. Well, I found the answer to that question on YouTube (natch). Here's the link to a really elegant solution:
Although they cut the flat pieces of the ridge-cap at a 45-degree angle, I don't think you need to do that. Just cut it straight but about an inch-and-a-half in from the edge, leaving the curved part as in the video. Then trim and bend it the way they do in the video and install as you would normally. Problem solved.
More later. They're working on plastering, textures, and coloring the mortar.