What material is the purlin for building?

Purlins for buildings are usually made of wood, and modern reinforced concrete buildings generally have no sloping roofs, so they are rarely used. In general civil buildings, indoor columns and beams are basically concrete structures, but in order to maintain the style of sloping roofs, wooden purlins are still used to adjust the slope of the roofs. Wooden purlins are still widely used in ancient garden buildings, but there are also examples of concrete structures replacing wood structures.