It is the ability to deal with tough weather conditions that makes a vertical carport design so appealing. Since the panels on the roof will be running up and down, rain and snow will have an easy path to simply slide off and down to the ground. That is not the case with a horizontal roof, which can make it difficult for precipitation—especially snow—to make its way off. For those who live in an area where heavy snows are a common occurrence, opting for a vertical carport is an easy choice.
It is true that a vertical carport will cost slightly more than a horizontal model, simply because of the need for additional structure required to finish the build. With that said, given the performance benefits gained by opting for a vertical roof, the added cost will be well worth it in the end.