Greenhouse ridge cap: How to?

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
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What about plastic guttering?
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David Hill
Abacus nurseries
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Do you want it vented?
Dave

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No, cannot be vented at top. Polycarbonate sheets already in place. Just need to put some kind of cap, in shape of inverted V, where sheets more or less come together at the ridge. I will explore plastic guttering suggestion but think Sundance suggestion (have local sheet metal shop make cap of steel or aluminum) will probably serve. Thanks for help. T-L

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Here is what I did on mine:
http://www.bunabayashi.com/images%20II/dcp_0014.jpg
Note that I have twinwall polycarbonate roofing as well. I went to a local sheet metal shop that specializes in gutters and flashing, and bought a length of copper flashing (approximately 20'). I had them bend an oblique angle in it and carefully got it home without crimping it badly. I then used the same gasketed screws that you use when fastening the polycarb to the structure.
Dave

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