Tap it with a screwdriver handle. Fiberglass will make a dull thunking noise. Aluminum will make a metallic, crisp pling.

If the inside of the stall area is not insulated, the roof's bottom surface should be visible. Most aluminum trailers are not painted inside. Steel trailers usually are to prevent rusting.

If you're unsure, scratch it with a sharp knife blade. If you see a dull whitish line, it's probably fiberglass. If you see a shinny scratch, it's metallic. If it's metallic, place a magnet against the surface. A reaction will indicate a steel skin, no reaction indicates an aluminum roof.

Gard