Heat Gain

The outside weather temperature under the trees in the tropical hot and humid climate is better than you think. In case an indoor environment feels unpleasant, it could be that the building design fails you.

Building material absorbs heat, store heat (thermal mass), and release heat from the direct sunlight into both the interior and exterior of the building.

Heat then can conduct through the air and reach our body.

The duration of a building material being allowed to expose to the sun is an important factor to determine heat gain of both interior and exterior environments.  

As a simple rule to prevent solar heat conduct through the building material and release heat into the interior, avoid sunlight directly contacting the building material, usually the roof and the wall. 

A few examples of intervention include the double-roof, big leafy plants or good size canopy tree shadings, a cavity wall, or a cavity roof. 

Consider thermal mass, conductivity, and density

If a double-wall or double-roof is unachievable, you need suitable building material that conducts, store and releases the right amount of heat at the right time.

Evangelisti, Luca & Battista, Gabriele & Guattari, Claudia & Basilicata, Carmine & De Lieto Vollaro, Roberto. (2014). Analysis of Two Models for Evaluating the Energy Performance of Different Buildings. Sustainability. 6. 5311-5321. 10.3390/su6085311.

Compare concrete, clay, steel, air, water, and timber. Water and air were brought to context as they assist a better understanding of the whole picture of the subject.
Relatively, concrete has high thermal mass, but low conductivity, high density. 
Timber has high thermal mass, low conductivity but low density. 
Clay has high thermal mass but lower than concrete has, higher conductivity, high density. 
Steel has a very high thermal mass, very high conductivity, very high density. 
Air has high thermal mass, low conductivity, very low density. Water has the highest thermal mass, but very low conductivity, high density.

Put in simpler relative terms: 

When solar heat on the materials, 
Concrete - Feels cooling, interior only gets warm after some time, but heat stores in concrete for a long time and release when the surrounding temperature is cooler (i.e., night time) 

Timber - Feels cooling for a while, but due to low density, the interior can immediately feel warm, will not store heat for long

Clay - Feels cooling for a while, interior starts to feel warm after a while, stores heat but not as long as concrete, cool down faster

Steel - Feels immediately warm, the interior feels warm after a while, will store heat for a very long time

Air - Feels cooling, starts feeling warm after a long time, will store heat for some time

Water - Feels cooling for a very long time, only starts feeling warm after a very long time, store heat for a very long time

Of course, the above consideration does not take air movement(wind) into consideration. Air movement will carry the heat or the coldness released by the materials away.
Design will determine the effect of heat gain on your comfort and use of spaces.