first the screenshots
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=603892802
The problem here is obvious the round wall doesnt snap to the foundation correctly, instead fly over it, even when placed.

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=607508749
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=607508804
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=607508825
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=607508847
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=607508878

now if you can see Im trying to build a place with a huge roof on top. with 2 foundation wide spread in middle between pillars.I know pillars act like walls. I I thought I could put my ceiling on both sides and close the top of the building by that. But it actualy doesnt work like that and refuses to be put in middle. ceilings always snap on sides or somewhere in middle of air even when placed. I hope I could explain my problem. sorry for that my english is not that good.