[Porsche-O-Phile]

Trust but verify...

Should have had an owner's rep available to handle the contract - it's very easy and a temptation for un-monitored residential contractors to pad their materials charges. Generally speaking it's better to get a lump-sum price up front (that can be evaluated for quantities as part of a simple descope) or have the work done on T&M but with oversight (i.e. field verification of what's actually coming onto the site and being used - do NOT rely on just invoices for "x" quantity of material (contractors have been known to over-buy by 10%-25% on several jobs (particularly for staple stuff that's used everywhere like plywood, nails, lumber, concrete, adhesion products etc.) then build up enough stock back at their yard to do another job without having to buy anything (or very little) for it - essentially meaning you and several other customers end up paying for your neighbor's project).

Most contractors are good but there are still an awful lot of sleazeballs out there - particularly in residential. Paying somebody who knows the industry a few bucks to oversee and monitor the job is short money against getting ripped off, and can give you someone else to go after if they don't do their job.

That said (I'll get off my soapbox now) you could talk to an independent third-party contractor or estimator and have them do a QTO (quantity takeoff) for your work and see what they come up with as a number in terms of square foot for material. Most places will price up something like this for free or they may charge a modest fee for it but it sounds like it might be worth the peace of mind.

Keep in mind that there will be some excess material required due to waste but a good contractor knows how to minimize that to keep his or her costs down. A REALLY good contractor will pass that onto his or her customers in terms of better and more competitive bids. If the contractor is using a few more percent of material then the roof actually calculates out to require it doesn't necessarily mean you're being taken for a ride - 5% to 10% is probably reasonable overage to account for waste.

Make sure they install drip edges, etc.

Good luck.