It looks fine for three chickens to me. Of course I would remove all of the pump stuff and fill the holes. Put down a thick layer of pine shavings, or whatever is avaliable in Thailand. Roost height is not to critical, I'd say 2 or three feet. I would leave the ventilation holes as long as the birds could stay dry in there. I would imagine your climate is similar to Texas or Florida. Lots of people in Texas and Florida have Brahmas and they do just fine. It looks like you could plug a fan in fairly easy, thats a good idea when its hot. A nest box is not really necessary if you keep clean deep bedding in the coop. I don't think cold winters would be an issue in Thailand?
Tim