metal roofing 5v or 2.5" corrugated?

Utility galvanized metal roofing for barns, sheds, etc. The 5v runs $15 per 8' sheet whereas the 2.5" corrugated runs about $10. What are the pros & cons for each type and is it worth the price difference?
The existing metal roofing started rusting at, and spread from, the nail holes punched thru the metal by the roofing nails. They were the coated nails with rubber washers made for installing that type roofing. Is there any way to prevent that when installing the new roofing? Predrilling maybe?
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I drilled and screwed, and calked.
Greg
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How large is the roof area in question ?
Using panel goods you will have the same problems eventually...
You should see if any roofing contractors in your area do standing seam metal roofing, almost all the fasteners in such roofing systems are located underneath the roof surface and the roof is held down by clips which hold tight when the standing seam is folded closed... Best thing is that if the contractor does enough of this type of roofing they will have a machine which will take a coil of the metal and form it into the roof allowing for a system with custom length unbroken panels from the eaves to the ridge...
Just an idea, less edges exposed means less leaks, less exposed fasteners means less rust in the future and a longer life for the roof...
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