As in a couple of the previous Alphas, it seems as if workers are building an extra layer of scaffolding over the already existing, and complete, frame when the roof is being constructed on a building.
As you can see, there is already the normal set of scaffolding covering the walls, like there always is. But, as work on the roof is starting, the workers seem to find a need to build an extra layer of scaffolding. At this point, there are usually some hearthlings that decide to build more scaffolding and some that decide to finish the roof like normal.
Sometimes, fortunately, the roof is finished before I run out of wood, but other times, I have to cut down a few more trees because the workers decide more scaffolding is more important. Then, they tear it all down and I end up with a surplus for my next building - which isn’t bad, until they do the whole thing over again and more trees are unnecessarily cut down to be used for unimportant scaffolding.
As one might infer, this is a bit annoying as I end up running out of wood before the roof is finished, and/or it takes a whole lot more time to build things. This never happened before Alpha 15 or 16, I believe whichever one was the first round of construction updates, but I don’t think it was as far back as Alpha 14.