It's possible to build a br from freerolls, I did it (and still play them when I can't be bothered to play "for real") until I got up to $50 which is a reasonable br to play $1 SnGs, then work it up.
BUT I've found that you won't learn much in the way of poker because a lot of FR players are rubbish or not trying, but also because the tournament structure turns it into bingo very quickly.
(Strangely, I think it was good practice for those late stages in tournaments where most of the players have 5bb or less, but that's no good if you can't get there in the first place).