I know that the Colosseum is about 189x156 meters, and 48 meters high, but I am having trouble finding any information on the dimensions of each of the 4 rows of seating. To be exact, where each row starts/ends. I can't seem to find anything other than very basic information on the dimensions of the structure.
http://www.tribunesandtriumphs.org/colosseum/dimensions-of-the-colosseum.htm This link appears to provide information on seat dimensions, arch heights of the 4 rows etc. Unfortunately, it didn't cite its primary sources.