Creating one clean surface from multiple overlapping surfaces!

Hi, I am trying to create several overlapping plane surfaces from plane curves, and would like to join them into one clean surface so that I can extrude them later.

My problem is trying to join the surfaces. I have tried:

[surfaces] -> [solidunion] -> [mergefaces]
and
[surfaces] -> [brepjoin],

however it still does not work. Could someone please give me advice?!
image and grasshopper file attached.

planar surfaces.gh (15.2 KB)

planar surfaces.gh (15.2 KB)

Hope this helps clarify my problem.

If you are starting out with curves, I think I had a similar question to yours and @HS_Kim found me the solution: