A dupe standing on level 1 building a row of tiles at the height of their head on level 3 will build the tile in the same space as their head, trapping them and leading to suffocation. Should the path-finding instruct the dupes not to build a tile in the same space they occupy or prevents them from pathing away?
Have dupes stand on level one. Plan to build tiles at height 3 where dupe head is. Instruct dupes to build it.