Thanks for all the help everyone! I was going about it all wrong, trying to fit me, some horses, and a school bus, all under one roof!
I've come to my senses thanks to KigerQueen and horselovinguy. I'm liking those PennyPinchers quite a bit!
Ponyboy: If I return to serious thinking about a custom build, I'll draw to-scale plans, using Adobe Illustrator. My one building from scratch went smoothly, but it was as simple as punching some things into the garage builder at Menards and a few days later a flatbed showed up with all the materials....I just had to piece them together like real-life Legos, using adult tools.
Staring at it, the only conclusion was, "there's no way I can make that happen with my budget ($100k-ish)." So, it was either the bus has to go, or I have to wait another year or two.
These kits look promising; time to keep digging. And thanks again for the insight.
(Does anyone else have a hard time understanding the audio thing at the bottom? Maybe I have more problems than not being able to figure out how to build a barndominium on my own?)