I worked out why one of my settlements was failing. I had renovated a house settlement and patched the roof by creating a collumn of foundation stones next to the house and then extending a structure of floor tiles over and around the house. It took me a full day but it was stunning and worth it. I would have used the only flat metal roof available ( the other that looks like part of an aircraft wing is quite useless - why am I melting down wrenches and screwdrivers to make aircraft parts?) but unfortunately while flooring has some flexibility, roofing has none. You can't stack floors with roofing forming the floor of the second level and the moment you bring in roofing into whatever you are creating everything around it other than a metal wall below it fails to snap in.

But within a few hours of opening this place to settlers the happiness meter plumetted. They had assigned tasks, pleanty of food and water and their defense was way above the sum of their food and water. They have all the advanced trading stalls all manned but still their happiness dropped. When they hit 4 happiness, it struck me. I'm sure the settler AI doesn't care if it is hot, cold, raining or shining so it is equally unlikely that they would appreciate the fact that they are living in luxury and protected from the elements by two layers of floor tiling and carpets. All they would factor is: "Is the bed I am using beneath category-roofing - if no, be unhappy." Well, I'm done. They can die or leave or whatever. If you don't care to make creativity work, why should I?

Wood structures has a better tile set with floors, upper floors, and roofs.