Actually, they can do that–That how I was able to pull off buildings like the Diadem Chateau back in Alpha 9. Since there was no system then for understanding how to make a lot of the construction “correctly” (most of it in various layers, not at once), the hearthlings used my stairs and placed ladders to navigate.
Actually, now that I think about it, the increasingly automatic scaffolding has hindered my ability to pull off some of these builds, since I often find myself waiting for unnecessary scaffolding to complete…