When will you have collected enough money?
I am talking about the time in future when you have collected enough money...
I guess future perfect should be used here.
Thank you for wanting to use my favorite construction: the future perfect!
Yes, that is the perfect usage (no pun intended). The time in the future when the money is collected is the time at which you will have collected the money.
It's a good usage of the Future Perfect. You can check yourself by making it a declarative sentence:
We use the future perfect to say that something will be finished by or at a particular time in the future.