01
Check suitability first
Have the roof's slope, support, and detailing assessed for the proposed slate system. The fact that the main roof uses slate does not establish that the same arrangement suits the porch. Discuss how the porch meets the wall and how water from higher roof areas affects it. Resolve those questions before choosing a matching color.
02
Compare at the viewing distance
Because a porch is often close to eye level, thickness and edge texture may be especially noticeable. Review samples against both the main roof and adjacent trim. If the same slate size cannot be used, agree how the altered scale will look. Record the accepted material and connection details separately so future maintenance recognizes the porch's distinct conditions.