Very popular in Morocco if that narrows your search. I think they use it to waterproof the walls of the hamams (baths/spas).

Hi, we're just finishing off a small ensuite with a similar shaped shower (photo) & decided to tile the sloping ceiling. Our builder & plumber said waterproof plasterboard & bathroom paint would be enough but we decided to go for the tiles & we're glad we did as the sloping roof does get wet. We tiled straight onto tile board which is stronger than normal plasterboard. We're still waiting for the fixed glass panel to go beside the shower door as the suppliers made it too big! Other than that, we're done. Good luck with yours.

I know PP rules are different n Scotland, but here in England in some local authorities it can be difficult to get permission for a new build that is as large as the old plus extension would be. If that is the case for you, it May be worth exploring how little of the old you would have to retain for the build to be classed as an extension. It might be as little as one wall, tho I agree the VAT savings are v attractive on new build.

Hi Cheddarmum we have just finished renovating our master bedroom up in the roof and have the same slope wall/ceiling issue. We painted slope and odd shaped wall as ceiling. It almost makes a feature of it in its own right! Hope this helps :)