01
Use the detail schedule
Ask the installer to identify starter requirements, ridge and hip arrangements, cut pieces, and any special shapes or sizes. Some are produced from field slate; others may need separate sourcing. The answer depends on the roof design, so avoid assuming a general waste allowance automatically covers every detail. Confirm the associated flashing and fastening materials as part of the complete package.
02
Keep the count traceable
List special items separately where that helps receiving and installation. Label reserved material so it is not consumed in ordinary field work. If a detail changes, revise both the drawing and the related order quantities. This small coordination step can prevent a nearly finished roof from stalling because the remaining stock cannot produce the required edge or junction pieces.