Regardless of the repair that you intend to do, there will always be a certain amount of waste of whatever material you use for the repair. If you need to build something, say with 4' x 6' sides, you will still need to purchase a full 4' x 8' sheet of whatever material you are using. Always plan for 5%-!0% waste for whatever the project is you are planning. Draw your project piece by piece to figure the total amount of materials needed.
David Elledge, April 2010