Purlins being intermediate beams running the length of a roof frame. Purlins need to be flattened to transfer loads from the actual roof.
I wouldn't be making just one purlin, but making an entire purlin array using the complex profile to create an extrusion fill. You'd use this fill as a wall, so it would turn corners - at roof valleys, for instance.
See :
complex profile essential learning
I see that you are new, but the idea of ganging up elements is important to productivity. You'd make a purlin set for each roof slope and span. The more you can do with the complex profile, the better.
Dwight Atkinson