As to the earlier question. I agree that with horizontal installation water pooling, wind and voided warranty are all considerations, water runoff being the biggest. As to the pergola inquiry, I had a ceiling fan installed, but with a screen house, I didn't worry too much about heat since we had shade and were going to use the solar gray color. However, we have since decided to use steel instead, because of the durability and ability to clean it and worry about the finish less. It's not as fussy to handle and install, either. That said, I can't imagine trying to fit corrugated roofing on a pergola because of all the tight angles. Cutting, closure strips, etc., would be a nightmare for us. We have 2 simple valleys because it attaches to a hip roof and that will be enough challenge for us! We also plan to use steel when we re-roof the house and garage next, so it will all be the same someday.