Anyone know what this flat silver area on roof is? Information, help and tips on many areas of roofing including trusses, tiling, venting, insulation etc....

[kev999]

I do hope you can help. I'm buying a house. From an aerial photo on Google Maps I see it has a rather strange shaped roof with what looks like a flat silver coloured area. Does anyone know what substance it would be, and is it likely to be a source of problems? And what would the darker L shape on the right hand edge be? Pic attached. I've never seen a roof like it before and would greatly appreciate any advice!