The main pre-occupation when designing for the equatorial tropics is to keep the sun and rain out; and to allow as much through-ventilation as possible.

These two requirements are however contradictory; the sun heats the place up but the rain cools it down.

A roof is needed to keep the sun and rain off one's head, but you also need walls to keep the inside of the building cool, shaded from direct sunlight and dry from the rain.

The introduction of walls would prevent any through-ventilation.