Thank you both.
After posting my question I saw the sticky at the top of the forum about pan size and the amount of batter!
Obviously that will help with the amount of batter.
I was a little surprised there were no directions for the cake -- I even own the magazine where the idea was presented and there is no additional info. Oh well!
I was thinking of using a 9" square pan and then cutting down an 8" for the top tier. Pretty much the same idea as what has been suggested. I will try and remember to take a picture to share.
Thank you for helping me!