Khun SeaT, I know you have many things to do before the rain gutters are installed. Boozer has a good idea but from the gutters I see here they are not very attractive, even the stainless ones you might see.

Another possible alternative is the Upvc or "plastic" ones. I see that the Windsor upvc window company here in Rayong also makes a line of the gutter products. I seem to remember that their prices were not too bad. I think starting around 325 baht/meter which is comparable to sheet metal in cost.