REINFORCED CONCRETE CONSTRUCTION
Although concrete surface is not vital with regard to the evenness of the the roof, the purlin and the material in between should all be placed so that they are all level, measured and on the same shaft. Both steel and wooden purlin and the material in between should be treated against corrosion in order to increase the life of the roof structure. Steel purlins should be welded into the material in between and the wooden purlins should be fixed directly to the wooden material in the middle.
The surface should be smooth, the top coating (OSB, etc.) material, even though it depends on the purlin distance, should be thicker than 11mm.
The angles of the steel construction should be controlled throughout the procedure since it effects the gradience of the roof. Divergence angles will result in a roof that is not even.