I'm familiar with the feature comparisons between standing seam metal panel
and conventional asphalt shingle roofing, but I have a few questions I
haven't been able to find answers to.

1. What are the differences (if any) in terms of airflow and insulation
required below the metal roof surface (below the decking)? Does the
decking get enough airflow from under the metal roof, or does a metal roof
still require airflow under the plywood as well? This would be over a
finished attic area, so I'd have minimal area for venting and I'm not sure
if or how this would affect my need to powervent or ridgevent to have
airflow. Ideally I'd love to use that expanding spray insulation to
insulate the attic roof space, even if I need to use those vent spacer
boards to leave enough airflow on the underside of the decking.

2. It has been a while since I've done price comparisons; what is the
general installed price per square (simple roof) as compared to the price
per square of asphalt? My old asphalt roof needs to be removed in either
case, so it would be for an install on just the decking. I'm not looking
for a to-the-dollar accurate answer, just a general estimate of how much
more I might pay per square if I went with something like galvalume (I
doubt I could afford copper).

Thanks for the info,
Keith