I think ICF would be pretty cool for walls, but haven't come across in the Philippines. Another option would be the extruded polystyrene (XPS) panels can be screwed directly to the concrete deck (or furring strips) and then plaster over like you would do a stucco style of finish. You can also put the panels on the roof deck, but then you are looking at a built up roofing that may be hard to source there. For walls I like the EVG panels, gives you some thermal value and fast to install. You could always go with block to fill in between the beams and columns and source the styrofoam peanuts and mix with your cement to fill in the cells of the hollow block...I'm curious to see how much of an R value you could get from that; probably would need to use 6" block instead of 4".
I love the flat roof idea for the usable space, using a lighter colored elastomeric roof coating will keep it cooler for when you are up there, keep the room cooler and also seals the roof...some folks will also use tile. Higher ceiling heights (9'-10') will also keep the room feeling a bit cooler.
Good luck and let us know what route you decide to go with.
Shawn