In replacing a roof, be sure all three layers have at least minimum standard materials applied and installed correctly on a sound structural system of rafters or trusses. Sheathing should be the same material as the rest of the roof and, in all cases, the same thickness of material when repairing only an area of roof. See Table 1, Fastener Specfications.
Licensed builders are preferred for roof repairs.
One test of their ability, if not their intent, might be to ask them to explain the terms used here. Adequate materials may be in short supply at a given moment. Substitution should be made only after checking with local or the nearest code inspector, architect, or engineer. Rather than accepting less than minimum standards of material, it would be better to tolerate patching until minimum materials and procedures can be obtained. A good repair job is required now to prevent trouble later and to avoid reducing the value of your property.