This is a question commonly asked by expats who decide to retire to the Land of Smiles and if you mean to physically build the house, this would be deemed illegal, as construction is a trade that must be completed by Thai tradesman. There are ways around this; you could, for example, hire a team of local builders and oversee the project (off the record) yourself, although you would need to be able to speak Thai.
Foreigners Cannot Own Land in Thailand
Aside from a few exemptions, it is not permitted for a foreign national to own land in Thailand; you can own a condo unit; indeed, you can own your own home, but not the land on which is sits. Many retired people choose to lease the land on a 30-year term, with the option of extending another 30 years. Another popular way to legally acquire land ownership is to set up a private limited company, with you as a major shareholder; the land is purchased by the company and is registered as such.
In the event you decide to set up a company to acquire the land, you must ensure that the company is actually trading; the Thai government have announced that any land procured by a company that solely exists for this purpose, then would repossess the land. It is critical that you are legally protected when buying or leasing land on which to build a house.
If you are determined to have an active role in building your dream home in the sun, everything is possible; talk to a local builder about the project and if you supply the blueprints, the team can build the structure. The Thai way of building is very different to what you would see at home and there is often good reason why they build the way that they do; you should have a good eye when the project reaches finishings and don’t be shy to point out minor issues, which can easily be remedied. You can find places with machine for rent (known as เช่าเครื่องจักร in Thai) if you are in need of equipment.
There are custom builders that work with foreigners who wish to build a home and they offer a comprehensive service and can even acquire land for your project. English-speaking architects ensure that you are happy with every aspect of the design and the builder offers a long warranty on all their builds.
We hope that you end up with your dream home and enjoy a long and happy retirement in Thailand.