If you've gotten to know her and you want to ask her to be your girlfriend, the best approach is a forthright, honest one.
Although it is hard to put yourself out there, because there is always a chance the other person will reject you as a dating partner, you won't know the answer unless you ask.
You've done all this work, the last thing you want to do is make her uncomfortable when you ask her out.
You can't get the girl if she doesn't know you exist.If she says no, tell her that it's okay but you probably will ask again. If she said no for any of the reasons other than that she doesn't like you that way, she may say yes next time.Worst case scenario, she'll be flattered that you like her and hopefully you can remain very good friends.If you are dishonest about who you are, she will eventually see that and will be hurt that you lied to her.Plus, you don't want a girl who doesn't like the real you, do you?
If you completely change who you are to get a girlfriend, she will have a hard time respecting you. Also, staying in your comfort zone will help you avoid those awkward situations where you put your foot so far in your mouth that you can never pull it back out.