Is it a good option to develop android games to make money?
If you are good enough and make enough of them, just remember that you are extremely unlikely to become rich by making games regardless of platform and you will have to work very hard or be extremely lucky to make enough money to be able to live off your work, It is a global market aswell so you do have to compete with skilled developers from developing countries who can afford to spend alot more time on their apps for a smaller return.
Its also a good idea to use a multi platform engine (or write large portions of the game using native code) to make porting to iOS easier as it lets you cover a larger part of the market. (WP7 probably isn't worth it at the moment unless you allready have a highly successful app due to its small marketshare but its worth keeping your eye on it to see if it takes off)