I am going to be constructing an outbuilding for livestock. It will be 32 ft. x 32 ft. I plan to use rafters instead of trusses. Is it OK to use 2x6's with 48 in. OC for the rafters at a 3/12 pitch? I will be using sheet metal for the roofing. Also, is it better to use decking on top of the rafters or 2x4 braces in between the rafters. I have added to pictures to explain what I mean:
The average annual snowfall in my area is 8 inches. The windiest month is April with the average wind speed at 7.2 MPH.