Some things to consider in rooms with high moisture content, particularly indoor pools that not only produce high levels of humidity, but with the water vapor, also contain corrosives (chlorine).
1. Water vapor will permeate through common building materials and condensate against non-permeable materials (plastic vapor barrier). Once water vapor has condensated in sufficient quantities, water will drip or run off.
2. Structures such as enclosed ceilings above high humidity prone areas will become collectors for water. This will encourage decay and fungus damage if framing members are wood and due to corrosive chemicals will deteriorate any steel present.
Many local building departments do not allow green board on ceilings due to initial weight and the capacity of nails to hold it in place. Water vapor will permeate the material and softening it with colapse eminent.
A better choice is cement board or cement plaster (stucco), finish smooth with a water proof coating as the final layer. A water proof coating such as UGL Drylock will cause condensation to occur on the ceiling and not within the framing cavity above. The key here is to provide the vapor barrier inside the pool room and not within the framing cavities.
Finally, provide good ventilation in the pool room itself to allow excess moisture to escape to the outside air. Even with good ventilation some condensation on the ceiling will occur.
Good Luck