I'm buying a condo on the top floor. The roof will be waterproofed (even tho not leaking) with a white resin material. Inside, is it better to leave the ceiling as high as it is, or put a new lower ceiling? Which is better for reducing heat in the room? Thanks.

Besides the waterproof system, you have to first find out the kind of heat insulating system that will be placed on top of the concrete flat roof, if any.

High or low ceilings, just make sure there is adequate roof insulation (and then more) because I have been to penthouses where the afternoon sun beating on the roof makes the temperature in the room unbearable, much like an oven. Even with windows open to sea breezes, it felt like I was sitting in a fan forced oven. When I was renovating, my builder told me the thin flimsy aluminium foil that they usually use is adequate and I stupidly believed him. I am not an expert but apparently there are very specific ways to lay them, not just bung them there...because one needs to consider air gap between insulation and roof tiles etc etc.

Although I have not used them (shopping for a supplier now), I have considered LOHR and ARC as 2 possible roof insulation providers simply based on their presence in Pattaya. I wonder if others have had experience with them?

High ceiling will help dissipate the heat. But penthouse / top floor units notorious for being hotter !!