This means that the largest square room you can have is 10x10 internal. Maybe there was a bug or that roof was not connected anywhere else. If you removed 2 entire walls and the corner between those two sides last then that roof was too far away from any other supports.
Gaga Rosco Rosco Collapsed Of Food Poisoning While Saving Him Gaga Was Knocked Out By A Mad Elk The Survived But Got With Images Food Poisoning Frostbite Knock Knock