I spent a significant sum of money a couple of years ago on this and a Sales Rep Agreement. I subsequently cut some things out of the original subcontractor agreement as some of the stuff was a bit overboard for some subcontractors. In my humble opinion, the primary thing a good subcontractor agreement does is subrogates responsibility appropriately. This was something our own GL and WC carrier required.
I share a ton of stuff for free, like the Roof Waste Calculation Workbook. But I've not shared legal documents and forms I've spent thousands and tens of thousands of dollars to have written by Attorneys. If you want to buy mine, make an offer. If sufficient, I'll share the original and the one I cut down a bit. I also can make no warranties or guarantees to the quality it may present to you or the validity with your local state, county, city laws. All I can say is it has worked for me now for 4 years in 4 states and 5 locations with roofing, siding, gutter, paint, drywall, flooring, windows, etc. subcontractors. We don't use any subcontractor unless they have WC and GL and sign the agreement, regardless of how small the job is.