How much paint will it take to paint over the roof, one door, a driver side fender and the tailgate.?

a lot depends on the color and what your trying to cover up also the type of paint to be used and the type of spray gun. a conventional gun uses more paint than one of the hvlp guns (high volume low pressure). conventional sprays more air causing more overspray where as the other sprays more paint and less air providing better coverage. a quart and a half verses 2 quarts, but you can usually purchase 2 quarts for a couple dollars more than the othe and have the extra pint