Without knowing a bit more information from you about the roof structure, and other loading information, it is difficult to give you an exact answer. This forum is probably not appropriate for too much discussion about a project specifics (rather it should be for generalities that can be applied to others).

But, generically speaking, a 6 x 12 #2 SYP spanning 16' spaced 5' o.c. can carry sips and standard roof live and dead loads.

Good luck with the project,

Joe