Roof sheathing is structural material that spans across the roof trusses or rafters, provides a diaghram for shear strength of the structure, resists seismic and wind loads, encloses the building, and provides a base for the roofing materials. When sheathing a roof, plywood or OSB can be utilized. The following are common panel thicknesses recommended based on typical spans:
Panel Thickness Max Span of Rafters
5/16″ 12″
5/16 – 3/8″ 16″
3/8″ 20″
3/8 – 7/16″ 24″
1/2″ 24″
1/2 – 5/8″ 32″
5/8 – 7/8″ 40″
3/4 – 7/8″ 48″
It is common for sheathing placement to start at bottom corner with successive rows being staggered.
Exterior Grade plywood may be required at edges of the roof if sheathing will be exposed for long periods of time.  Otherwise Exposure 1 or Exposure 2 sheathing may require protection. Panels should be laid perpendicular to rafters. They should be jointed 1/8″ for expansion purposes and this is often achieved with plywood clips.
Panels should be nailed with 6d common or ring shank nails for panels up to 1/2″ thick and 8d for panels 5/8″ to 1″ thick. If the top chords of the trusses are warped or bowed or the rafters are not plumb or square, they will need blocked or shimmed. Fasten nails at 6″ spacing on all edges and 12″ spacing at all rafters and never within 3/8″ of a panel edge. A chalk line may be used to indicate nailing rows.
It is common to protect the sheathing from rain/snow damage if it will be exposed for a longer period of time by installing the roofing felt right away.