They did not get to scaffolding, as they have not finished the floor. I have not had problems with them building up against a mountain like that; Hence many of the structures all around Sorenia that I have made. As of A16 all structures within the place they have been able to build.
A17 I am confused why they didn’t even start for the most part. Especially when they have not gotten to the scaffolding part. I have a couple of buildings that have been built like that in Sorenia up against a large rock, where there is a gap partially on one side. And yes I had to “babysit” but to me it is more like just helping out.
When they don’t get even that far, then I have to wonder what the actual problem is. Dealing with scaffolding placement and helping them along is the easy part when they get that far. Ladders do wonders.
Maybe I’ll see if I can get them to build it in A16, although unsure if the blueprint would work; since that was made in A17, which means I will have to remake if the case.
Most of my building usually have foundation for the exception of a couple buildings, and when I do one without, this happens; even if the other one worked. I’ll have another look regadless sometime later, but I am sure there is something a bit more to it than scaffolding placement. The stone floor with a clay border might be the problem, but that is just a guess. 
@Doc_Brano Well with this building style I have not had much trouble with this type. Free standing would look odd with what I have in mind… In a way this is technically pushing the building limits. The way I see it, I should be able to build this, as the rest of the town is buildable. I could understand being a bit aways from the rock that is attached to the mountain if it were the wooden roofs or the stone ones, but these clay roofs are generally flat along one side. The little bit of wood sticking out has plenty of room; I made sure of that in the very least. I’ll check later though if free standing will. Even if it can, that just means I have to redesign it so it will build in that specific nook/location.