Circular / spiral stair

Hello,
does anyone have experience with modeling circular/spiral stairs using polylines copied in -Z direction, than creating a lofted plate? The unfolded drawing of the lofted plate looks strange. What is the correct workflow?
circular stair external plate.gh (12.1 KB)

The goal is to model these stairs using 2 bent plates (bent in 1 direction) on left and right side of the stairs - stringers.

Thanks in advance.


Sorry, I forgot to mention, I use the Curve+ plugin from Food4rhino and the Tekla Structures plugin.