How about a building where you donate money to it and then it converts it into a unit or bonus.
EX: you donate 20mil to the building and it converts the money into maybe a 500/500 unit or maybe 5% building output.
The more money you donate the better bonus or unit you get! The minimum amount of money you can donate is 1mil and you would get like 10% building defense or something crappy. The maximum could be 500mil and it would make maybe a 7000/7000 unit or -15% health regen! It would take a week to convert the money to a bonus or unit.
What does everybody think?