This seems to be a case of two planes fighting over the z-index. Would changing the floor thickness of the grass level to be lower than the house level floor thickness result in the room's floor being drawn above the grass?
Unfortunately, no. Thikness of level goes in the downward direction; so upper Z-s are still fighting.
Each house is always above the ground and it's one of the good practices.
If second (building) level is higher then grass even on 0,001m you cannot see on the one plan both levels, only the top one (building without grass).
But in my case both level are needed on the plane, like here
Now I draw every room by hand, like here, but it takes a lot of time:
