Hiring A "Contractor"/Carpenter

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My Thai honey, who lives near Roi-et (Isaan) has some land that I plan to build a small bungalow on so when we visit her family, we have something private to stay in; thus, I am not putting all my savings into the structure. It will be around 80-90square meters... 1-2 small bedrooms -- with one Western bathroom (tiled) and a small Western kitchen. The basic structure will be rectangle with a simple A-line gable roof (just in case we want to add on some day. Here are some questions ... She has a relative that has worked on temples and houses. He is recommended to be the builder/contractor. His costs are 70,000 baht. I have no idea if this is reasonable or not; meanwhile I am told that we could build a house of such for around 600,000 baht. I realize that the kind of windows, flooring, lighting , cabinets and such has a lot to do with the price after the "basic" structure is built.

Is it best to give the contractor a blue print or give him a design and have him deal with the details. ( I realize this is different than in Europe or in America).

Of course before I make any final decisions, I want to see the work he has done.