Hello there; You can download the Steel Structures regulation from the official gazette and the Implementation guide from the website of the Ministry of Environment and Urbanization. S235, S275 and S355 are in common use in materials. It will be more economical to choose the type of material that the most of the products in the market are, as far as we know, the most commonly used S235, but it will be more convenient for you to keep in touch with the company that will make the application. You can find the material table of Section 2 of the Steel Structures Regulation below. Good work.