If shower walls will be custom floor to ceiling frameless glass, what material should be used for the ceiling?

We are building a new home (new construction) and are having the bath tub and shower removed from the master bath, to be replaced with a custom shower. The shower will be enclosed with a wall-to-wall, floor-to-ceiling frameless glass frame and door. The glass will be held up by a 12″ soffit coming down from the 8′ ceiling, and the interior shower ceiling will be 8′ in height. The builder has suggested that they are not planning to tile the ceiling, but that it will be a higher-quality type of drywall than usual. They said they are not planning to tile the ceiling in case there are any plumbing problems in the future (so it would be easier to get to the plumbing: one detail is that we will have a rain shower head coming from the ceiling in between two standard heads). I am concerned that the ceiling will peel and become damaged by condensation and steam…