I built my new deck last year nad want to start utilizing the space underneath it. My deck material is Geodeck composite, Geodeck told me that I can use an "underdeck" type system without voiding my warranty. Instead of paying the higher cost of the underdeck system, I was going to use steel roofing with the white side down to add some light to the area.
Here's a video of someone doing something similar to what I'm thinking except I would run the angle mounting boards for the roofing the other way.
I'd appreciate any how-to's or comments or suggestions on my idea.
I guess I don't care for the look of the corrugated vinyl used in the video, especially with the exposed edge. It doesn't look finished to me. I believe the Underdeck system is integrated with a gutter. I suppose you might be able to terminate your home-made system with a piece of Azek trim, and attach a piece of gutter to the inside to achieve a similar effect.