Brandon:
Go to this site and page: http://www.beamchek.com/publications.html

And download this free booklet called: "Introduction to Load Paths and Wood Design. You download it by clicking on the link that says: "View the Acrobat pdf version." It is a pdf file.

This explains load paths and how to calculate loads.

Basically rafters are considered by their run as the snow load is vertical. The snow load is the "live load" on the roof.
The dead load is figured by the length of the rafter. You combine the two to make the "total combined load".

Then you can adjust things for "snow duration" based on the type of roofing used. Snow slides off metal roofs when they warm up.
So the duration on a metal roof is less then on an asphalt or a wood shingle roof.

I hope that helps you to understand load paths.

Jim Rogers