01
Compare more than the dominant color
Look at the wall's light and dark stones, mortar, surface texture, and visible trim. A roof that matches one stone closely may compete with the wall's overall pattern. Ask the designer to compare a quieter roof option with a more varied one using representative material.
02
Keep the decision reproducible
Photograph the sample arrangement with labels, but retain physical samples as the primary reference. Record the selected slate, its acceptable range, and the associated metal finish. If the wall will be cleaned or repointed, explain that planned change before choosing the roof. This prevents a selection made against a temporary appearance from becoming an unexpected mismatch after other work is complete.