Best roof for tropical climate
I'm a big fan of corrugated steel roofs.  They are noisy in a rain, especially if you have the windows open, and have little or no insulation in the ceiling space. They are quieter if they are firmly attached to mass:  E.g. a steel roof over 3/4" OSB over trusses will be quieter than steel over 2x4 purlons over truss.  

Steel roofs are commonly done on trusses at 4 foot spacing here for machine sheds  Roofing fluctuates a lot in price, but my latest shed it was 2.35 Canadian per running foot 3 feet wide.  Call it 80 cents per square foot.  They last about 40-50 years.  Nowadays you can get them in a large variety of colours.  In a tropical climate I would get white, or very pale yellow.

In a tropical climate I would consider very oversize trusses so that you have and 8-10 foot overhang all the way around.  This reduces solar heating, and gives you a bunch of outdoor space that normally doesn't get wet.