Thank you all for the input, and I welcome any additional!
I'm adding these suggestions to my research bucket. I thought about steel for a while, but I haven't looked at the cost. I never thought about fiberglass.
Over the weekend, I was looking at videos on natural buildings with earth block arches and also "super-adobe" (more info on that here --
https://www.calearth.org/tour), and it looks like you can do dome and arched roofs. I might actually build a small dome shelter to get us through winter after we purchase land to build on. It seems that it's a really quick, low tech, and low cost way to get a solid structure with thermal mass up. Then I would plan and start building our main house where I'm more concerned about the roof structure.