Closing / cleaning up offset and cap on forms

Im trying to cap my offsets so the forms can become walls but I’ve made a mistake somewhere on my caps and they are capping the inside verses just the offsets. Can anyone help me clean this up? I would also like to only cap the ends on either side of the forms or “tunnels” but right now its also capping things in the middle.

Opera hall form file 10.8.3dm (228.0 KB) Opera hall form file (22.4 KB)

Red group…

Opera hall form file (25.9 KB)

Thank you for the solution for the end caps. would you be familiar with how do connect the offsets into capped walls? Another issue thats troubling me is the end of the arcs on the offset dont go down all the way so can’t connect to the bottom offset of the form.