Many years ago the price to build this was just over 2 million baht, nowadays if done to plan it would be around 2.6 million baht, BUT, nobody having a house this big spends only that, they don't want 100baht light fittings, this sort of house normally has a fitted kitchen, fitted bedrooms, doubt they would want the 150baht a box of tiles priced for their floor, probably marble, granite or teak wood, something like this to finish and fit out nicely is going to cost 6 to 7 million, original plans has no roof insulation, maybe you would want double glazing etc etc etc. this is the ground floor floor plan, has a few utility rooms and a Thai bathroom and a farang one, upstairs is 3 bedrooms and 3 bathrooms.
You can download the full architects plans for this building here Luxury Thai House Plans 3 bed 5 bath.zip