Boat roof material?

If you encapsulate the plywood in epoxy; there is no reason for aluminum sheeting. The epoxy, protected from uv by painted canvas requires no assistance from aluminum. And the aluminum will make the roof an improved thermal conductor, aka hot as Hades.

Forget the aluminum. It would be used in the absence of epoxy. If you want to use the AL to protect the edge of the plywood; it would be far easier to glue on a wood radius with thickened epoxy.

A carpenter shop can easily build you those parts and once glued on; you can easily roll some epoxy over the edge to seal.

The aluminum will not end up looking good at all on that radius.

Make sure and sand the entire top to give the epoxy a place to bite the ply. Shiny paints are used as release agents for epoxy, and the paint itself can shear.

I advocate for foam because things like the edge (radius) can be formed easily.

 

I like the aluminum sheet idea. I'd not use contact cement to bond it, but use a polyurethane (goo in a tube) or epoxy to bond it. It wouldn't be difficult to skin the whole thing in a single sheet and lightly hammering over the edges to radius it off, for some screws or nails, which would be covered with some trim. 29 gauge will be light, easy to cut and position and will protect the existing roof from UV, forever, which is a long time, assuming any and all cutouts, notches, hardware mounts and fastener holes are well bedded. Roll down the sheet into whatever you use to bond/bed it to the roof and it'll look fine.

 

If it was me I would use marine ply, hot-coat with a couple of coats of epoxy, fill the edge grains (including holes)with thickened epoxy and paint with UV tolerant white-paint. I finished my bait-board this way, using grey mist rustoleum as the paint. 5 years later - there is no visible deterioration.

In the case of your roof panel I would protect any vulnerable edges by gluing on a sacrificial beading of some kind. On my bait board I cut my knife and tool slots over size and glued alloy to the edges of them.