I'm playing around with a couple online calculators trying to determine what material would be needed to frame a roof. Its high time i figured out how to do this myself, but there are a few things i dont understand. What does deflection refer to, and how do i determine it? How do i calculate snow load for my geographic region? The roof i'd like to frame is 6:12, and the run for the span is 13'3". I think the bare minimum i can use is 2x10 hemfir on 24's, or 2x10 spf on 16's. The rafter length is around 18' with the 1' overhang. Can someone point me to an easily understood reference to show me how to clculate this myself?