It depends entirely on whether you are planning a single or a two storey house.
From the pics it would appear that Nawty has used what are often called an RSJ - Rolled Steel Joist, which is a heavy I - beam also used for lintels. It was probably the most reasonable solution in the rather special design of his house.
The steel that is used in Thailand for ring beams and purlins in single sorey houses, is usually box section, 2 x 4 x 3.2 which is available in three grades ranging from 500 - 1,500 baht per standard 6 m length.
Some engineers choose to used two C-section girders welded face-to-face to create a very strong 4 x 4. if you are building a single storey house, there is no reason whatsoever to have a concrete ring beam, which is very much more cost and labour intensive. If you are contemplating a span of over 7 metres or so somewhere - such as to aviod a central pillar in the middle of a large living room - you could install a concrete beam just over that part, but doubling up on the steel would still be easier and cheaper and just as effective.
Some building contractors cut corners and ignore the engineers' specifications. Instead, they use C-section beam for the ring beam, and after the tiles have been laid, the weight squashes the open ends of the beam together causing the roof to sag. Not a pretty sight - and extremely expensive to remedy.
If your house is an unusual design, your best bet is to consult an engineer or talk to a well informed agent of the CPAC company, or just get the CPAC roof installation handbook which explains what to do and what to use without baffling the customer with science.