I like this girl and were friends but I don't know if I should tell her that I like her?

Don't actually tell her
Just drop subtle hints and flirt flirt flirt

You should just ask her out on a casual date. Any girl who has any respect wouldn't say no to a first date. Then when you guys go on your date just see if she is being flirtatious or if she is just kinda there. If you can't tell which one it is just tell her that you like her, confidence is an attractive quality. If she says that she doesn't like you then you know and you can just be friends.

No DONT DO IT! You will get stuck in the friend zone. If you really like her. DONT DO IT! Just keep hanging around her, let her make the move. And don't buy her any flowers don't confess that you like her, and don't write her any stupid I love you letters. They don't work!

Well first I'd like to figure out how long you've known each other and been good friends. How much do you talk to her and hang out with her? (if you don't then I would begin) I would say that developing a strong friend-level relationship is a great basis for going to a higher level with her. (I know, it's not what you wanted to hear) By doing this it shows that you care for her as a person and not that you're wanting to jump into a deep boyfriend/girlfriend relationship right off the bat.

As for you being shy, all I can say is that you got to get beyond that. Know that if she doesn't make a move, you don't make a move (even a small one in your case) NOTHING will happen. You got to realize that if you want to have a chance with her you put your shyness aside. Deep down in you got to know that your fondness of her has to be greater than your social disabilities.

For now, don't worry about what to say to her, but when you do tell her how you feel. Make it implied, meaning don't say "Do you want to be my girlfriend?" Tell her how beautiful she is and that you love her personality. Say she is perfect and tell her how much she means to you. Like I said, don't think about that now. Just be friends.

BOTTOM LINE: Being in the friend zone at the moment is the BEST option, if you become closer to her, you will develop a chance to grow your relationship.

Don't tell her anything. Start flirting with her and being more attractive around her. Attractive as in emotionally attractive and stimulating, not just physically attractive. Be desirable.

Girls aren't stimulated or drawn to friends or friendly guys.
And nobody is 'attracted' to someone confessing their feelings without the feeling being mutual.

Give her something to be interested in other than a 'nice guy who is her friend'.