I never looked into the fancy under deck systems as someone told me it was expensive and my dad confirmed after research.
We used metal roofing upside down (many colors, mine matches the trim on the house). I made a lattice of treated 2x2's to give it pitch. Then ran it all to a gutter on the steel beam supporting my deck. Very happy. Paid itself off when I drank my first cold beverage under it in the rain.
Great thread BTW, looks like fun.