You want advice on how to make a girl like you as more than a friend? Sorry to be the one to tell you this, but it doesn't work that way.... you cannot MAKE someone like you as something they don't want you to be.
Having said that, if your friendship is as good as you say, then two things apply:
a) she probably already knows how you feel about her. Women are annoyingly good like that.
b) it can't hurt to talk to her about it. She's your best friend - you should be able to tell her exactly how you feel. You'll probably get the "I like you but only as a friend" line, but that goes back to what I said at the start. You can't make someone like you, without pretending to be someone or something you're not. Or, of course, she might say "Really? I feel the same about you, i was just afraid you didn't want that. Let's get married." That's what you're hoping for, and I'm saying ask for her, see what happens, but don't expect much.
Good luck, and remember this is only my opinion which doesn't ALWAYS mean it's right
Let us know what happens!
CasperTG