Extrude surface perpendicular

Hello, I have extruded a surface in z-direction. Now I would like to extrude it perpendicular to the surface. I have tried evaluate surface but can not get it to work.

Thanks!

q_gh_extrude_perpendicular.gh (4.6 KB)

Like this?

q_gh_extrude_perpendicular_re.gh (10.0 KB)

Yes, thanks! I solved it by using offset…