The roof decking could be the layer of plywood or O.S.B. nailed to your trusses or rafters. Roof decking is often seven/sixteen” and comes in 4’x8’ sheets. Should you’re tearing off previous roofing, the roofer can try to find injury that needs to be repaired once the deck is bare. https://portaltrendz.com/4-roofing-contractors-recommended-in-oswego-il-top-local-experts-for-your-roofing-needs/