Not sure if it applies the same in your area, but metal roofs that are not insulated will condensate and drip up here in Nebraska/Iowa. When installing my roof I also applied 1/4" thick foil faced foam before the metal. I know it was overkill, but I actually installed 7/16" OSB then the foam, with the metal roofing on top.
No drips or leaks in 16 years.
It is amazing how even 1/4' thick foil backed foam really does reflect the heat from the sun. I also applied it to my sidewalls before installing the steel siding. In hindsight, I wish I would have wrapped the sidewalls with OSB as well.
Note: The OSB was way cheaper back in 2006.
John
