Traditionally roof substrates are made of CDX plywood. However the glues used in manufacturing the CDX plywood gas off slowly and impact many canaries, despite being covered with underlayment above and insulation below. A safer product is corrugated metal decking material, 20g typically. This is available in custom cut lengths similar to standing seam metal panel roofing. Other alternatives to CDX plywood is 1” tongue and groove roof boards. Roof boards avoid the glues used in plywood. For structural strength, hardwoods should be selected. As roofing boards have been displaced by the use of CDX plywood, you may have to have the boards specifically milled.