Well all you would have to do is make a minimum limit on the number of cashiers or ATM's. Then all that has to be done is check that NPC can reach the cashiers or ATM's ... just path checking.

I think a good idea would be player designed vaults or security systems. This could be a mini-game or could be represented by contracts in a game. Say a bank offers you a contract to design their security system. They have a budget of £100k and certain components cost so much (bank vault door £10k, ...