as far as a scale goes, I don't think that a 10/10 in my eyes is possible purely because that would have to be complete perfection and everyone has faults.
Its much easier to use a number scale rather than list the qualities that make somebody beautiful because of the aspects of both time and the fact that an attractive quality in one person might turn out to be an unattractive quality in another.
Anyway, to me the saying 'beauty is only skin deep' is pretty accurate, I judge beauty as a physical manifestation with very little to do with personality, that comes later.
I really like this question. Obviously there are many different aspects of beauty when looking at a person both mind and body, but for some reason everyone (myself included) is so hung up on physical beauty. For me, physical beauty is based off of body proportions, facial structure, and skin complexion (not color--complexion!!). Those are probably the biggest things when I personally look for beauty.