I'm currently in the process of building from freerolls.
There are a few ways to do this.
Qualify for CC games.
This is fairly obvious, CC provides great freerolls for members and you just have to make 65 quality posts. Once you qualify you get to play twice a week on fulltilt. Then you just have to play enough to make a deep run.
Other Private Freerolls
Keep an eye out for any private freerolls with a descent payout. If you can easily qualify, then there is no reason not to give them a try. There's only one other private freeroll I'll play besides CC games.
FT- Sit and Learn Freeroll is great... 5000 dollar prize pool. 1500 entrants and the top 540 get paid. This just happened yesterday, I finished in the top 180 for 7.50. Runs once a month, quailfy by completing a FT academy Sit and learn.
Build your play chips
Grind your way to a few million play chips, and then play the daily 500k 40$ freeroll. Fairly easy to cash, 60-90 play, 18 get paid.
Best way for me to build play chips was through the step tournaments. Work your way to step 7 and then just keep repeating the process inorder to gain a reasonable amount of play chips.
Public Freerolls.......Maybe
Worth a shot, but their a crapshoot. My best finish was 5th or 6th out of 7500, it took 6-7 hours and I got 6 dollars. I got lucky, and whoever else cashes in these also get lucky. That's all public freerolls are, luck.
I've been doing this for a year or so. I play all of the freerolls listed above, besides public, I gave up on them. Right now I'm sitting at a BR of $20.40. Made most of that over the last few days grinding 2nl. It's possible to get aBR started, but there will be many days when your BR sits at 0.00. All you need is one break through, run good run from a FR cash and your set. Hopefully I run good for awhile to build a reasonable BR from my freeroll winnings.