Prefab steel buildings

Since your in MI, you're going to want to pay attention to the snow load rating. As far as span goes, my pole barn is 36 feet wide with no supports. Living in South Texas, there really isn't a snow load rating required, but if there was, they can make a truss that will carry the load. Usually, you'll have a local code requirement that the building manufacturer can design to. There are also wind ratings if that is a concern. mine was required to withstand 115 MPH, some require 150. These aren't willy nilly numbers and are spec'd to maintain a safe structure.