How Do I Internal staircases on foundation

Internal staircases on foundation

I have visited MikeInsides page which is awesome, but everytime I follow the guide to do this, I end up with a whole in the side of the house. Please help. Anyone has any ideas as to what Im doing wrong?
I am supposed to use the boolprop cheat and it works, then I follow the guide precisely as instructed, then turn the cheat off again, and I end up with a big gap in the house.

 

Close this post, I figured it out.