The roof decking will be the layer of plywood or O.S.B. nailed into the trusses or rafters. Roof decking is usually 7/sixteen” and is available in 4’x8’ sheets. In case you’re tearing off previous roofing, the roofer can search for damage that should be repaired once the deck is bare. https://nicehomeliving.com/5-roofing-companies-customers-love-in-downers-grove-il-top-choices-for-service-and-quality/