A problem in the construction of the wall (RimWorld)

Crawling the network and not found a solution to this problem.
During the construction of the wall gives the message This area will not sustain such a construction is. Build from different blocks and useless, still the same. What with the roof and without it, still does not want to put in these three blocks.
Even using developer mode, cleared the area, so the ceiling collapsed, because the settlers are not always able to get him off the mountain.

Spoiler