Creates purlins onto a rectangular area. The script is designed for the generation of purlins onto the roof of a warehouse building with multiple frames. The purlins are connected to the substructure with links. The definition of the plane of the roof, number of the frames, section of the purlins and other parameters can be done through an input dialogue after the start of the script. It is also possible to mirror the generated purlins, which can be useful in case of duopitch roofs.