Hello
I think freerolls can help build your bankroll, but I certainly don't think you can build a big bankroll just by playing freerolls.
What's more, I understand that
poker sites do not allow you to make cash withdrawals unless you deposit in advance.
In other words, only by playing freerolls you will not be able to withdraw cash.
Now, what you can do is play freerolls and take practice to dedicate yourself to this, start growing your bankroll, and at a certain point be able to make a deposit to start making withdrawals, because the site, even if you only play freerolls, a Once you deposit those funds they are already considered cash in your account.
Greetings