Dead air space is a common problem. The easiest remedy is to install air sofets under the eaves of the structure. These sofits need to be evenly spaced along the perimiter of the structure to ensure proper air flow. This can done by anyone, but I would recommend using a professional roofer.
you can usually install yourself or hire someone to install a blow foam insulation of some sort. Most are made from soy and is a pretty good insulator.
Dead air space in metal roof acts like an insulator. All seals should be secured to make sure that it provides proper insulation and hence the desired R value.