01
Ask for the basis
Have the designer or qualified professional identify the project requirements and review supporting product or system documentation. Ask which slate dimensions, fastening arrangement, substrate, and details the evidence covers. A supplier's general statement may not answer how a particular roof edge, corner, or attachment is to be designed.
02
Resolve the actual installation
Keep the accepted design and instructions aligned with the material being ordered. If a component or fastening method changes, obtain review before work proceeds. Retain the final documents and relevant installation records for future maintenance. The practical question is whether the specified roof is supported by appropriate evidence for this building, not whether slate can be described with a single all-purpose wind rating.