Do I Need Planning Permission?

In Thailand the official answer is YES. You need the exact same permission as you would with any home. Planning applications must be submitted to the local authority together with plans signed by 3 notaries (Architect, Structural Engineer, Local Councillor)

Many areas of Thailand will also have regulations on the type of foundations required for a particular area.

If you are located on your own land in an area of the countryside then the rules will be a lot more flexible and maybe no one will pay much attention, however if you are based in a major city then any construction work would likely be visited by a local inspector within a few days.