The issue of the "squareness" of a building reminds me of a time many years ago when I was working for a small research company located in a colonial era New England house. One large room in the house was the library, which had a ceiling probably about six feet and six inches high at one side, tapering to about five feet ten inches on the other side. I could tell, because I was about six feet two inches tall with plenty of clearance on the high side of the room only.
When the house was built, I suspect that a tall guy worked on one side of the house while a shorter guy worked on the other side, each using his "elbow to finger tip" as a measuring device. In spite of this peculiarity, the house was solid, having lasted over two hundred years when I worked there.
Hmmm. Maybe a little Photoshop wizardry could fix that house.