£12k? Presumably that was for genuine Welsh slate (or maybe Spanish) or is he replacing all the rafters and purlins wiith rainforest for that? There's a bunch round here been leafleting £3k for strip, refelt, bonding gutters, new battens, fibre cement slates & dry ridge. Suspect they'll make a load on salvaging the old slates (not a realistic option on yours if they're covered in goo). Unless you're in a national park or something you'd be mad going for real slate- yes it looks beautiful but it costs between 6 and 12 times what mock slate costs. Especially if you're going to flog the place.