Describe what is visible
Metal can be exposed, plated, painted, or otherwise coated. At a distance, several systems may look alike. Begin with sheen, panel size, seams, and visible edges. An exposed cut or folded corner may provide a clue, but it is not permission to scratch a finish or lift a panel.
Color is especially unreliable in photographs of reflective surfaces. A gray panel can mirror a blue sky or a red wall. Make a second observation in different light if the distinction matters, and keep any proposed material identification tentative until a reliable source confirms it.
Track the path of water
Streaks often begin at a fixing, lap, projecting edge, or adjacent material. Follow the path upward as well as downward. A stain on one material may have come from another. The shape of the mark can suggest a question, but it does not prove a cause.
Pay attention to the base of a panel and sheltered recesses. Rain exposure and drying conditions differ across the same elevation. A broad label such as maintenance-free hides the importance of detailing, environment, and the actual product.
A reference is not a specification
Record the date, weather, orientation, and visible assembly. Pair a close image with enough context to relocate the detail. If you find manufacturer documentation, record the precise product and document date rather than substituting a generic metal name.
For selection, repair, or safety decisions, use current project-specific advice and verified performance data. The purpose of a visual material study is to ask better questions and recognize relationships, not to certify a building from the pavement.