Is Roofing an Art or a Science?

Of course, both, but it depends on whether you're talking about the installer, the salesman, the company, or the manufacturer. The Greeks debated the virtue of the beautiful versus the useful until the cows came home or the fat lady sang, depending on which happened first. About dusk it was difficult to tell them apart anyway and after a little Retsina, the mooing could be confused for prose.
In my universe, the installer must concern himself with beauty because the useful has been outlined in his training and work order. He need not understand the nuances of where exhaust vents are to be placed, he must just place them where his bubble map says.
The salesman too need not concern himself with actual placement. His job is to come up with numbers of how many intake and exhaust NFA inches are required. He and the homeowner determine which system of ventilation is to be used with the salesman, better the technician, knowing which are to be discarded from the box of options and which are left on the table. The salesman is the liaison between the homeowner and the manufacturers. His books and samples open the homeowner to the numerous options of color and style (beauty) and weights, warranties, and impact resistance (useful).
Through studies of preferences and buying habits the manufacturers constantly tweak their product line's colors and shapes. They watch their competitors and if another company has a smash hit, the designer knock-offs begin. The knowledgeable sales technician asks the right questions and helps the homeowner wade through his options to find the right look. These guys need to be artist's assistants and mathematicians.
The roofing company provides the training to put on a good long lasting roof that saves energy, if the customer likes saving money through products with high emissivity, reflectivity, and hail and wind resistance.
The manufacturer makes good products that are appealing.
The roofing company chooses the product lines its salesmen/technicians offer based on its history of experiences and then trains its force to design practical systems and look for associated problems. The company also trains its installers on the most up to date methods and demands efficiency from them.
The salesman walks the homeowner through his options based his desires and needs and shows him the systemic options available and most suited by budget and need.
The installer follows his orders and picks up his mess. He must be neat and considerate of the property.
The owner teaches, worries, and studies.
If everybody does their job the roof will compliment the house and the home will be more comfortable. The roof won't leak, the roof will last longer than the neighbors roof of the same quality, and everyone will think the house handsome. A good roof is like a nice haircut. The shape of the head is made nicer by a good artisan.
And if all fails because Chavez sold bad oil and the asphalt is not right, then all is good because the homeowner bought the extended coverage available from all certified contractors.
If your contractor is not certified by a manufacturer then you are out in the cold if problems occur. If you read the warranties you'll find that after five years a roofing product warranty is pretty lame unless you use a certified company and follow the suggestions offered by the technician.
GAF, Certainteed, and Owens Corning have great programs. Be sure and ask if your roofing company has a certification. If it doesn't then you might consider very strongly of choosing another. Tamko makes great products but they don't have a program, I assume, because they don't want the liability of non pro-rated 100% material and labor warranties and prefer the old school pro-rated material only one.
As far as Atlas, Malarky, and Pabco, you are on your own from day one. These manufacturers seem to be completely lacking in any moral fiber. Protect yourself.

www.jonwrightroofing.com