DIY Shed & metal roof install – GreenBuildingAdvisor

Hi all. I’m going to be installing metal 5-rib panel roofing onto an 8×8 shed. The rafters are 24” OC and I have installed 3/4” plywood for sheathing due to snow load (Ontario Canada), followed by synthetic roofing underlay. The shed will not have heating or AC. 

I’d like to add some kind of strapping to the roof sheathing for better hold on the roofing screws. Will strips of 3/4” plywood work (I have some sheets leftover), or do I need 1×4 lumber? I was considering 2×4, but don’t like how high it brings the drip edge off the fascia. Which brings me to another question…does the strapping have to go over the sheathing or is fastening from underneath between the rafters possible? 

Thanks & appreciate the advice