I do alot of work with CFS (Cold Formed Steel), which is what you're talking about. CSD's advice is spot-on. You don't want to try and calculate the strengths yourself.
Good luck,
YS
B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...
But the same people who give you the load tables, etc. will be able to give you the dimensions and section properties, which you may need for other reasons than strength.