Fabricate and install a piece of solid surface material for a ceiling. It can be a solid color that matches your tile or grout, no additional vapor barrier is required, and no grout lines to clean - ever.

Trebuchet - thanks, I had not considered that idea. What do you mean by "solid surface"? Do you mean Corian type of materials or like an acrylic type of thing like shower walls are made of?

I would probably just repaint the ceiling. Unless the plaster is falling down or loose.

It's not necessary to tile the ceiling (it's an aesthetic choice). If you do tile, it's not necessary to use a moisture barrier, or even cement board. Is the ceiling plaster? Is it in good shape? If it were me, and I were going to tile the ceiling, I'd either pull down the plaster and put up drywall, or put a sheet of drywall over the plaster.

BrianKK:

Yes. Some Corain and other solid surfaces are available in 1/4" thickness, but you could use 1/2". After fitting, clean the substrate and the back of the sheet and apply half-dollar size dabs of silicone every 12" or so. Jam some pre-measured props in place (use blocking on the ends to distribute the load) and leave them for a day then tile up to the solid surface.

Thanks, Trebruchet! Will do some research and pricing. Thanks for the tip!