Springfield heights 2 billion
There were glitches early on in SH that allowed people to have more than 10 of the mansions, etc.
Forum Discussion
Even if you don't, you can keep farming materials and spending the base materials (furniture, coffee, mats) and get several million per day. Add that to the amount you get from upgrading all of the buildings and you probably could get there without the glitches.
Why you would bother though is another issue.
Why you would bother though is another issue.
