Bank

I think that clash of clan should add this.
Lets say I have 3000000 gold now but i need 4000000 gold to upgrade my wall. So When I try to upgrade the wall I will not have enough gold and they will prompt us to use gem right? Idea: Instead of just prompt us to use gems, they should allow us to have another prompt called BORROW,when we press the borrow button, 4000000 gold will be removed and instead of my resource level being 0, I will have -1000000 gold.
However this will not be abused because there will be limit, the limit will increase as your storage level increases.