this is the thing I don't understand. is it shaped according to his hand or sth? or just the standard shape with his desired size?Federer's custom handles are probably molded to fit his hand exactly the way he likes it to fit. It may also be made of a different material than the stock handles.
I've bought many retail racquets that are supposed to be and indicated to be the same size grip but in actuality when you hold them you can tell they are not the same size. The variation can be pretty large at times so that a 4 1/2 may feel more like a 4 3/8 or a 4 5/8. So the pros get their handles custom molded to insure that they are all the same exact size that they like so that each one feels perfect to them.