Well, if you are going to share your feelings, realize you are doing it for YOU and not necessarily for the answer he gives. I mean, yes, it would be awesome and wonderful for you if he said yes. But, he might not. So don't tell him because you must know what he thinks and are hanging on his every word, do it because you feel comfortable and ready to tell him.
Also, you may not get a yes. So be prepared for whatever answer you might get, and the possibility the friendship could change or, in worst case scenario, end. Not to be a Debbie Downer, but it is possible.
So be careful about how you want to do this. I'm not saying obsess over the perfect moment, because that almost never works as planned (nothing in relationships is perfect, anyway), but be relaxed and open about it. Try not to build tons of tension (at least not enough to overwhelm you), but try and go for it when you are relaxed and alone together. Remember, he is still your best friend. Yes, you are telling him you like him and it may not end as you hope, but it's much more possible you will get a straight-forward and compassionate answer from him.
I say take this chance if you feel ready to. You know, people try to hide feelings for best friends, but it usually comes out some way or another. Better if you aren't plastered at a party and scream it out before falling down the stairs.
So, just be yourself (I cannot stress that enough) and be confident. You are an amazing person and you're ready to open up. Whatever happens, it doesn't make or break you. You will always be wonderful as you are.
So go tell him!
And good luck.