I used ACL. Aluminium Composite Laminate.
It has a few other names as well, but is a product commonly used in the sign writing industry. It is also being used a lot for cargo trailers and truck bodies. Here in New Zealand we have it available from several manufacturers, usually in 3mm or 4mm thicknesses. It is made up of (in the case of the 4mm that we used), a sheet of about 3mm plastic composit, with about 0.5mm of aluminium laminated on each side with painted (or powder coat) finish on both sides, or with the sheet I used on the roof was white on one side and "mill" (bare alloy) on the other. The side sheets we used were red on one side and yellow on the other, we used the red side. The sheets come in a variety of sizes from the usual 1220x2440 (8'x4'). I used 3m x 1.5m sheets for the sides and a 4.8m x 1.5m for the top. This one went from the drawbar all the way over the roof and down to the bottom of the hatch.
It is rasy to work with, it curved over the roof and hatch easily and if you want to put sharp bends in it you just rout a groove in the back of the bend. Cutting is easy with any sort of saw or a router, or you can use a Stanley knife and snap it. l used jig saw and a multi tool.
Would I use it again? Without hesitation!
I was easy to cut, just glued on the sides, top was glued with screws around the perimeter, covered by the alloy trim.
It was really quick as once it was cut and glued on it was finished.
As it is used in the sign writing industry, it is made to withstand the out door elements.