IMO if you like the girl, don't tell her you want to be friends first or anything related to friends...just enjoy the time. If you mention the word friends and she actually likes you, she will think you don't really like her and possibly move on. Just keep it to yourself. Now if you truly ONLY want to be friends and nothing more EVER, then you can tell her.
PS if you really like her but want to take it slow, just let her know you like her but TAKE IT SLOW...don't make the moves lol but if SHE makes the moves, make sure you stop before it gets too crazy and let her know that you truly like her, but like her enough that you want to take it slow although your body might not want to...