The design of most pole barns is simple. Poles make up the outer walls and support the roof system, usually pre-engineered wood trusses with a roof sheathing. Poles are usually spaced 8' apart, with the trusses bearing directly on the poles. Some variations in design call for truss carrying beams between the posts with trusses sitting on them. The exterior walls consist of girts attached horizontally to the post with the exterior sheathing attached to them. Exterior walls may be finished with corrugated metal, plywood sheathing, vinyl siding, or other cladding. Roof materials are generally corrugated metal but may be finished using any typical roofing product.