LOVE your mod and thank you for all the hard work. I have been spending a lot of time with it lately and here are some suggestions to add more functionality.

1) More inside corner diagonal roof support. Maybe just have the E key mirror the outside diagonal corner? Couple other inside diagonal right and left corners maybe too. My appologies if I am missing something on this.
2) Diagonal doors, gates and archways
3) Allow railings to attach to ceilings without a foundation check. Currently, you have to have one less ceiling out in order to put a railing on it.
4) Windowed roof tile
5) Add a config to allow for more ceiling support from foundations.
6) Vines

Also I have one question, why are your foundations and blocks slightly smaller than vanilla? It makes it very hard to mix and match with other mods and vanilla blocks.

Nitpicky stuff mostly. This mod is amazing!