Yeah, for whatever reason the game isn't applying the appropriate normal maps to those textures. Looks like it's applying the Bren, MG42 and PIAT normal maps to the roof. I've seen this before, and it happens way more than it should. It usually happens to the soldiers for me, though.
OT but Rambler I want to thank you for your great Trees and Bocage mod!
Its still the best one around as far as I am concerned and it looks great with Aris' terrain as well as opposed to the more subdued trees and foilage.