For my GH restoration project, in which I have put twinwall
polycarbonate in an existing aluminum frame, I installed a flexible
ready-made cap from Lowe's by screwing it in three overlapping sections
to the aluminum cross-pieces, and, though functional, it looks like the
devil: uneven and ugly.
Sundance Supply offers two other options:
1. 15 mil Butyl Adhesive Roll Roof Flashing Tape from Carlisle
Hardcast; I would want the 6 inch width with shiny aluminum foil
backing. Sundance Supply says this will work at polycarbonate roof
valleys, but I don't see why it wouldn't work at the ridge as well.
2. Go to a local sheet metal shop and have a cap made from aluminum
(.019" minimum) or steel (30 gauge). Sundance says aluminum is easy to
fasten and cut but flimsy. Steel is sturdy, harder to cut, and requires
pre-drilling prior to fastening.

I would appreciate opinions as to how to cap this ridge. Thanks.
T-L