You're playing 1c/2c. Unless you are unable/unwilling to deposit, you don't have bankroll concerns. Even if you are building up from
freerolls, your bankroll limitations are not going to be defined by the more conventional ideals (# of buy-ins, risk of ruin, etc.) because you have no ability to move down. You are stuck playing with as many buy-ins as you have, until you are ready to move up. If you can't/won't rebuy and only have $10 online, then you are playing with 5 bullets--without regards to any other bankroll considerations.
On top of that, bankroll is
not limited to how much you have online. It is the amount of money you have set aside, or are willing to contribute, to poker. If you are willing to add $20 a month (or whatever), from your income, to poker then that counts as part of your bankroll consideration as well.
I am pro-depositing, despite having built bankrolls from freerolls before. Building without being willing to deposit takes a lot of luck and patience. Even following Ferguson's rules (which are decent for building from $0), you'll spend the majority of your time down below $100 and then find your bankroll grows pretty well after that. You can keep building and busting a $5 roll (from freerolls and cash game variance) for months, or skip that and just add $20 a month until you are growing the bankroll each month from your play.
Edit: If you deposit, eventually the goal is to never sit with more than 5% on any one table. Even less than that, if you are playing higher and/or games like PLO where variance is higher. But, until you have $40 online, you are almost always going to play with more than 5%. And, you'll move up when you get to $100 or $150 (depending on how much you are ready to drop down).
Edit 2:
http://www.pokerlistings.com/online-poker-s-greatest-challenges-pt-2-jesus-turns-0-into-10k <- link to Ferguson bankroll rules
You'll note it took him 9 months to get from $0 to $100 (and part of that was luck in binking a tournament for $104). After hitting $100, it only took 9 more months to get to $10,000. And, he's probably a lot better than most of us. Getting stuck down below $100 due to stubbornness is horrible. I forget exactly how long, but it took me well over a year, at first, to break $100. It was probably closer to two years. But, I was at the point where I refused to deposit and was going to build from nothing. I did it. I wouldn't do it again. I would just play like I had a $100 bankroll, and be willing to deposit if I had a bad run.