Do you want to drive in the high side of the roof, and have it slope away, or drive in the side? If you need a large enough opening for a car to drive in, you might want to consider a post frame design, with 3 trusses, or more if you want to hold more vehicles.
As far as snow load and wind load, the truss designing software will size it appropriately.
This is a simple 20 x 20 from the Menards site.
