While it is a bit of luck, this was my end game. I started out investing in curses and other units before investing into buildings and stat boosts to put my units up to 9/20 (which is typically when they become undefeatable in standard battles if they have a shield). Once I reached that point, I just farmed for the same building... which is easy since the building allows me to farm for more buildings, creating an endless loop of cash.