The title is self-explanatory but just to be more precise.
Once a building is finished I can’t seem to find a way to add things (let’s say a built a manor and want to add a wing). Even if I could just build a “new building” next to it, the main problem is usually the rooftops. The only option is to build a sort of “corridor”, with a flooring as roof, that connect the building but I need to have built the previous building with a door already where I want to connect it to something else, otherwise I won’t be able to even add a door to a wall.
On a related subject, is there a way to efficiently build “internal” walls without screwing with the roof placement? I find that pretty much always if I plan the building with a not-so-common shape, the roof placement goes to hell. To give you an example just think about a T shaped building with an internal wall to divide the vertical space from the horizontal. I still am trying to understand how to build it without the roof messing everything up.