Ok, So you wanna win lots of money on the roulette? Well, i'll show you how
LEGAL NOTICE (!!!): This is illegal, And therefore this guide is only for educational purposes Me,Nor D3scene is responsible for any illegal actions that this guide may provoke
Notice nb2: You Will get caught if you do this in a real casino, and you will get caught if you try to win 20K dollars so please stop before 1000$ 
Now this is really easy, yet efficient (Note that you must have a large start sum, just in case if you loose much at the start).
Lets say you start out with 100$ (you wont need that much but its an easy nubmer

Pick a color (lets say Red (its red or black ya?) )
Now what you want to do is to start betting Ex: 1$ then if you win you bet 1$ again... easy right?
But if you loose you double your bet, so if you start with 1$ and loose, you bet 2$...
Why? Because then you will always win the double of what you lost

easy right? now the only way to loose money on this method is by quitting when you are loosing...
Code:
Resumè:
1: Start with some money in the bank
2: Bet 1$
3: If you win, bet 1$
4: if you win, keep betting 1$
5: If you loose, Bet 2$
6: If you loose again, bet 4$
7: If you win bet 4$..... Get it?
8: QUIT WHILE WINNING!!!!!!