Permanent use of the property

Here, reference must first be made to Thai law.
We have put together a few important basics for you.

The general rule: Foreigners are not allowed to buy property in Thailand. Exceptions are linked to high conditions that are not explained further here.
Nevertheless, it is possible to legally use a property permanently.

Possibility Number 1:
Foreigners can purchase 100% of flats or apartments for residential purposes in multi-storey buildings. The total living space of foreign buyers may not exceed 49% of the building.

Possibility Number 2:
The foreigner concludes a lease or rental agreement with the owner of a property. This is valid for a maximum of 30 years, but can be extended to a maximum of 90 years.
It is important to agree on all conceivable changes (inheritance, building rights, sale, death, etc.) in writing and to register the contract with the Land Office within 3 years.
If all requirements are met and the contract is concluded accordingly, the leaseholder / tenant can use the property as they wish.

Possibility Number 3: 
Land acquisition through a Thai company in which they have an interest.
However, this is also linked to high legal hurdles, which probably do not apply here.

If you are interested in "own" property with a self-erected house, we are happy to support you.
This includes in particular the procurement of a suitable plot of land with the necessary activities in court (including a Thai law firm) on site.