I used the Arcs you already had (white group).
About your loft and extrude operations: “That’s one way to do it.” (wrong)
edge_boundary_2020Aug28a.gh (27.7 KB)
i attempted to do it all all one piece and make the middle piece cut through it to separate them but im fairly limited in my knowledge with grasshopper. I tried using the other arc commands but i couldn’t un twist the lines and they were not attaching to their opposite pair on the other side. I learned how to do it from watching videos on 2 organic curves but it did not work the same when i tried to apply it to the shape of the lines i drew. Thank you very much for your help, i saw that you helped me with my question yesterday as well and i appreciate it.