What do you think about fiberglass panels?

I want to build a 5' wide Benroy, and am considering covering it in fiberglass. I found 4x8 panel at Lowes http://www.lowes.com/lowes/lkn?action=productDetail&productId=8566-293-77096&lpage=none
I could cut the 8 foot length to 5 foot and lap the panels together on the roof. Does anyone know of a good, clean-looking weathertight way to make a fiberglass panel lap joint?
I could cut the 8 foot length to 5 foot and lap the panels together on the roof. Does anyone know of a good, clean-looking weathertight way to make a fiberglass panel lap joint?