I use matting that is designed for horse paddocks. It comes in various thickness. I have 3/4" material. It is heavy rubber-tire type substance. This roadway shown has been outside continuously for more than three years. I frequently walk on it. This was bought at TSC. Farm supply stores like Atwoods also cary the material.
JimC.
John,
Shingles and rolled roofing are both a fiberglass mesh base impregnated with an asphalt material. Shingles are usually a bit thicker than rolled roofing too. Asphalt shingles were probably originally designed to emulate slate roofs.
Bruce,
Pond liner tape would probably do the trick to seal sections together. It could be put on the underside. It comes in a 6" wide roll and is very tough, flexible and sticky. It is a bit pricey too.
-Brian