Roofing and Stress skin panels

I will soon be doing a roof for a friend in Illinois. It's a hybrid timberframe. The main body of the house is a 2- 1/2 story 10/12 pitch frame made with King post bents. My concern is the panels on the roof. They are made up of 1"tounge and groove spruce, 4-5" foam,and 1/2" plywood.
When my company stocks or puts bundles of shingles on roofs, we load the whole job at once. Normally on a steep roof such as this we use a 12' or 16' 2x4" nailed through to the rafters. Question, Seein as how I wont be able to nail through the panels in this case, I need to figure out a way to keep them up there. Lotta weight, those 2x's will just tear right off the roof.
Another question, same problem. When putting my hooks or brackets at the bottom will the panel hold my weight, plus a square of shingles? Yikes!
Once again, Normally I'd put the 16p nail in a rafter and feel safe, but I dont think 1/2" plywood will hold all that.
Any thought s or experience please write me, here or at JGYOGA@aol.com Thank you JG

The assumption is you are using good quality screws to fasten the roof panels to the frame. Cleat safety is achieved by using a few of the same screws to hold your 2x cleats. When finished use the drill in reverse mode to remove the cleat screws and then replace the screws in the same holes.
Work safe.

Yes definetly use the screws to hold you on the roof. but be careful there maybe ELECTRICALwire ran over some of the timber. And a good panel screw wil go thru the safety plate.
I've had roof jacks come off before and shingles and I went to the ground. We always screw down and try to get into the timber so you don't scar the exposed decking.