I am trying to construct a Nautilus spiral staircase in sketchup, but not having much luck in using the TIG extrude extension to construct the curved and twisted balustrade, see illustration below, I couldn’t build the surface within the highlighted wireframe. I found it easier to use the ‘projection tool’ in rhino, but again, I don’t think I have got the right answer to how to construct this surface for the spiral Nautilus geometry. Helix is easier but not sure how to do Nautilus, could anyone please share some knowledge? many thanks!!!