Glad you're enjoying 😊
The inside thing is a bug. If you have 4 walls, and want to add a door, if you hover over an outer grid cell and rotate the door into the wall, it will not be detected as part of the building. Same thing for windows. So it's possible to have a building with windows and walls and to not be detected. We found this bug a bit too late, so we just updated the objective text with a hint which hopefully helps the player avoid it instead of fixing it 🙈