they require scaffolding on base floor not on constructed floor
they build scaffolding on both sides of interior wall but you only see one side unless your in full building view mode even further if you turn the camera the scaffolding will switch to other side at a certain point of view if your not in full building view mode
roof wont be started unless interior walls are constructed on both sides if one side is complete and the other is not in build mode if you rotate the camera the wall will disapear at a certain point of view changing it to preview wall while not in build mode the wall will look constructed from both sides
due to the necessary gap between buildings prevents closed walls although i have placed a door on the inside while in placing doodads but I did not construct it with the door on the inside the base of the door is still ground level but virtually it should work you still have to have the floor connect to each room to make it one building