There's an english idiom, "rolling in the dough" which means you're currently very rich. ("Dough" is slang for money.) Idioms (like the one at the end of your sentence) are used playfully, but the first part of your sentece is very direct, like a command. The two intentions don't match up well in the same sentence. I would say something like, "Don't worry, just pay me back when you're rolling in the dough." Or, "You don't need to worry about paying me back until you're rolling in the dough." There's definitely more than one way to correctly express this sentence!

I would NOT want to wait until the person was rich - it might take too long! I would usually say, "Pay me back when you have the money."

You can pay me when you have lots of money. Or - you can pay me when you have become rich.