01
Order by the work sequence
Ask the contractor which sizes and accessories are needed first and which roof zones follow. Graduated or patterned work may require particular pieces at particular stages. Confirm that a later delivery will not leave the crew unable to complete an exposed section. Keep the agreed blend and product identity consistent across the purchasing documents.
02
Track what remains outstanding
Maintain a simple record of quantities ordered, received, accepted, and still due. Ask the supplier how later lots will be matched to the original selection and review any proposed change before shipment. Avoid treating the first delivery as proof that all remaining material is secured. Update the schedule when supply or site conditions change so the roof is opened only in coordination with available resources.