House-building

I’ve been trying to build a nice cabin deep innawoods, but I’ve been running into one minor problem… I can’t keep the rain out. I’ve got all I need to build a roof, both regular and sodden, but I simply don’t get the option to do so. When I built my door, I noticed that I could build a roof, but only in the small one-tile space that would have been my door.

What kind of wall formation do I need in order to make building a roof an option?

I think you can only build a roof if at least two adjacent tiles are buildings. So, you need to start in the corner so that you have two adjacent walls, and then you should be able to build one next to that, and so on.

Correct.

Related note: if you plan on opening up the walls (say, to build a vehicle through 'em), it helps to build another wall segment nearby to ensure there’s still enough support for the ceiling. Collapse-checks aren’t quite as stringent as build checks but can be more of a pain.