A flat concrete roof for your Philippine house? Here are a few things you should consider.
The flat or nearly flat concrete roof is an irresistible draw. It vastly increases living space at a little more cost than a conventional metal roof. It seems unlikely to blow off in a typhoon. But, most appealingly, the flat concrete roof can be used as a high patio with privacy, breezes, views and so forth. If you do decide to have a concrete roof, I suggest you support the concrete using galvanized steel deck forms. These metal panels look something like galvanized roofing but heavier. The panels serve as a permanent steel base for poured reinforced concrete floor slabs. The need for temporary wood forming is eliminated. The panels are supported by the concrete beams.
The concrete roof is appealing idea but we advise caution. The sun will heat the slab all day and then re-radiate the heat into your house 24/7. We have a friend who built a house like that with the idea of using the roof as a patio. The house was pretty much an oven and the patio unused. Most of the problems can be overcome but with additional expense. The patio can be roofed or partially roofed to give some shade both to people and to the roof itself.
An insulated ceiling can be installed below the roof, but these add to the already high cost of the concrete roof. There is no ameliorating the fact that having a slab of concrete high up in the house is a hazard in an earthquake. Not only could the roof come down on the house inhabitants below, more importantly the tons of high-up weight can magnify the pendulum-like lateral sway of the entire structure, especially in a multiple-story residence. If such a roof is decided on, be sure your engineer designs the structure below to accommodate the additional stresses.