My Apologies to all for "Falling off the edge" and not replying.
I finally solved it, and hope this helps others.
I had the same problem on 2 other projects, and solved it by checking every polyline on every Roof Plane -
make sure your "Angle" box is "Point Zero" - 0.0, 90.0, 180.0 270.0, and for Hip Ridges - 45.0, 135.0.
Thanks for all your suggestions.
Best Wishes