This is intended behavior (in fact now we have bugs where crafters prioritize building or mining over crafting their recipes). So it’s better to not promote many people at first, if you want to build faster.
Normally when newcomers face with that many building errors, is because their building shapes are hard to build at the moment, or not supported.
You should always take into account that there should be enough space for the scaffolding. Right now there are sometimes when the scaffolding will be built on the inside when it’s needed, but I think it’s still buggy. If you make a floating stair out of slabs, it will probably throw some errors or demand manual scaffolding in order to be finished.
Too many stories also can be problematic or laggy to build. Interior walls are still not supported. Sometimes you have to build part of the building first and then add other part after it built (e.g.: adding a slab staircase after having finished building the house).
You can’t edit buildings after they’ve been built, other than placing furniture inside the rooms or adding slabs here and there in the building or placing ladders or something.
And sometimes the building tools just get bugged for whatever reason, so the best is to report the bugs here with a screenshot of the bugged building (and a template or savefile if available), and steps to reproduce the errors. It really helps the devs.
Also, we have a topic to post buggy building shapes 