Under Thai law a foreigner may not own the freehold to land. However, a freehold title for a building which sits on the land can be purchased. There are a number of different purchase options available to the overseas buyer and most property developers will offer buyers both freehold and leasehold alternatives: 

Purchasing the land leasehold and the property freehold. The land on which the property sits can be purchased by a foreigner as leasehold. The developer will lease the land to the purchaser for a period of 30 years with an option to extend, at minimum cost, for a further two 30-year periods to give effectively a 90-year lease. A good leasehold contract should include a clause which states that if the land law in Thailand changes, making a freehold option available, the title may be converted from leasehold to freehold at the leaseholder's request. 

Land Titles: Land can have different titles in Thailand, depending on factors such as the location or whether it can be leased to a foreigner or not. There are seven types of land titles but just three of them can be leased: Chanot, Nor Sor Saam Gor, and Nor Sor Saam.

Purchasing land through a company: Another alternative is to set up a Thai Limited Company. If you decide this is the best option for you, be aware that as a foreigner, you cannot hold half or more than half of the company's shares. Therefore the company has to be at least 51 per cent owned by a Thai citizen. They can then choose to sign over their company rights to you. Note that the Thai Immigration office is aware of this kind of procedures and will certainly monitor your business.

The property that sits on the land may be purchased by the individual or a company such as a BVI (British Virgin Islands) company set up by the buyer. It is usual for the purchaser to set up a BVI company that holds the lease on the land and the property freehold title. If the BVI option is taken it makes the resale process very simple as the company can simply be transferred to the new owner and changes to the land title and lease are unnecessary. The reasoning behind creating a BVI company is that it can lower potential company taxes for an individual, but it is not always necessary to do so. 

Source: http://duensingkippen.com/publications.html

*Please note all advice given here is strictly informational in nature and should not be considered serious legal advice. Before attempting to purchase property as a foreign national, always consider you options and seek advice from a licensed legal professional.