Don't know if this will help you or not, but Home Depot offers something on their website under the PRO tab. I think it is sponsored by Anderson Windows and the name of it is called superbuild; but everything is by line item. There is a section there on roofing and once you plug in the numbers, you can go to reports and then export it to Word or as a PDF file. From there, you could make the "proposal" or "estimate" into an invoice with just a little bit of re-wording.
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