My walls are 8" concrete with the 2.5" of foam on either side. With
the 4' footers, the walls are actually 20'. Done in two pours. There
is a 2x10 sillplate and standard rafters. It is sided with steel and a
steel roof. Interior is done with OSB and drywall.

ICF is very flexible. You can build curved walls, odd angles, etc. It
is almost easier than "conventional" construction. Plan everything
ahead. While not impossible, it is very difficult to add "holes"
later.

My supplier, www.integraspec.com There are many different ones.

I have a bunch of photos somewhere. I will have to repost.