placing the heavy cooking part of the kitchen outside will always work in Thailand ????
you will have to think about details such as smoke/exhaust management, easy placement of cooking supplies, roofing, etc.
regarding the drain in the floor, yes, Thai bathrooms usually come with that drain in the floor, but Western bathrooms usually don't.
I mean building the whole bathroom floor with a very slight slope that guides the water towards the drain. The bathroom floor could also be 1 cm lower than other floors. The Japanese generally make very clever bathrooms.