Well, Fossil, dimensions, and resolution depend on the graphics work you needed and size of a vehicle. Some people use normally dimensions around 78"x52" @72 dpi. If you want wraps for trucks then you may have to increase its size. Remember, you will have to go with the unique/custom design approach in order to gain customer trust and future service requests. Now, people are more concerned about the promotion of their services or products and they go for the vehicle graphic and wrapping services.
You can read a guide on the type of vehicle graphics essential for business promotion here : See a type below in the image.