Bankroll

I don't know about you guys, but there are some online sites that I have a horrible time trying to build a bankroll. Two of those sites that I have difficulty are the most popular (for US players), those being PokerStars and Full Tilt. No matter what I do, I cannot seem to build a bankroll from a small deposit ($50). Whereas on sites like Bodog and Pacific it does not seem to be a problem. I was wondering if anyone had an suggestions for bankroll building on stars or tilt???