There's some very useful info in this thread. My opinion is it's all about shade and ventilation - as much of both as possible. Keep the sun off the walls or even better, don't have walls, just a covered area. Besides shading, trees are naturally evaporative coolers, pumping water from the ground and releasing it into the air. Insulation is useful, but if used incorrectly can trap heat, particularly in upstairs areas if the ventilation is inadequate. The tradition style was uninsulated, which cools quickly, but is unbearable during the day, so ppl stay under the house and then move upstairs at night to avoid the critters and possible get a cool breeze upstairs.
Concrete driveways trap heat. It's common to see houses where the whole block is concreted for ease of maintenance. Besides storing heat, I believe they contribute to flooding in Pattaya and probably elsewhere.
Roof and ceiling height are also important, I think 3m should be enough for shaded areas, but am interested in others opinions as I am also designing a house.
Blinds are also useful for keeping sun off windows or out of shaded area at certain times of the day, to be rolled up later for more air flow. I like the matchstick blinds. We soaked ours for an hour in borax and they've lasted a decade. Made from natural materials they allow for ventilation.