The roof decking will be the layer of plywood or O.S.B. nailed to the trusses or rafters. Roof decking is usually seven/sixteen” and is available in 4’x8’ sheets. In case you’re tearing off outdated roofing, the roofer can hunt for destruction that should be fixed after the deck is bare. https://portaltrendz.com/4-roofing-contractors-recommended-in-oswego-il-top-local-experts-for-your-roofing-needs/