The load on a roof includes the dead weight of the roofing material, plus snow, and wind load. Since you have not indicated where you live, and you have given little information about the geometry and materials, it is not possible to provide a meaningful answer.
The Following User Says Thank You to Daniel Holzman For This Useful Post:
Will, Welcome to the Forum. I see this is your 1st Post and you have a post question.
We are here to help and will do our best to answer your question. This is the best DIY site but as Dan pointed out there are a lot of factors to consider in making your decision.
Take a look at this somewhat related Post in that the question involved the use a 4x4 post and illustrates some of the factors that you may not at first thought of: