A bloke I work with was convinced he was going to make his fortune doing exactly this until everyone said what a fool he was.
If you want to make money from betting you really need to put your money on something that you can realistically predict,like football matches,etc.
Roulette is a game of chance and online roulette is,in my opinion,potentially fixed. Because after all all you're doing is playing a computer game. How do you know what's going on inside the program?