List and interpolate curve

Hi there, Im trying to make a relatively basic model and am being trippedu by the list function. I have attached an image of the structure I am trying to make but would would really appreciate an explanation of the list function rather than a script to solve my problem. 

As you can see the structure effectiveley 2 semicircles in plan, joined by arcs spanning across. What I need is to be able to Isolate the necessary points to join from the list, then create an interpolated curve so that i can change the height of the structure

Thanks,

A