These so called roulette systems never work!
I saw one once where you monitor the column the number came up in, and start betting on that col after, iirc, 5 spins of it not coming up.
Each bet covered the previous bet, until you hit a max (I forget what), and then, you make a loss on that run.
With the "free" money that the casinos offer, you may think it'll work, but I wrote a quick simulation to test it.
I can it several times (basically, picking a number between 0 and 36 randomly, and betting with the system), and it busted each and every time.
And, this was with a starting balance of $500 ($250 your money, $250 bonus money).
Like others have said, each spin is independent of the last, so, just because X hasn't happened for X spins, doesn't mean it's any more likely to happen in the next spin.