I'm fidgeting with a build myself and wanted to pop in and let you know having a basement isn't a requirement. I just have a habit of adding basements to most of my builds. lol
Ohhh speaking of the roof I had a heck of when I was trying to do the roof. I am not used to working with the octagon roofing, but was able to work something out that I am very proud of.
I don't really have any tips on roofing other than play with the different angled roof pieces to find which one will work best for what you're trying to do.