I have some roof deck damage on a small shed. It's a standard plywood deck with asphalt shingles, and I'd have repaired it the same way by now if access weren't a bit tricky.

But it got me thinking.

When we lived in Europe courtesy of the Army all the roofs were clay tiles. They didn't have a roof deck covered by moisture barrier covered by shingles; the tiles were wired to the battens or rafters (I'm not sure of terminology) and they could be worked on from underneath. A mechanic would unwire a section and step through from the attic to fix an antenna, etc., then wire it back. They never leaked. They did sometimes blow off in a big storm, or get cracked if something hit them.

Not that I would put a tile roof on a shed.

But you could almost simulate a tile roof just by splitting some plastic pipe, maybe in the 4 to 6 inch diameter range, and overlapping. Roof tiles are about 20 inches long normally, but there'd be no reason you couldn't use standard ten foot pipe lengths. Alternate face up and face down, and there should be nowhere for water to get in.