The NZ Metal Roof and Wall Cladding Code of Practice is a comprehensive design & installation guide, and a recognised related document for Acceptable Solution E2/AS1 of the NZ Building Code.
Black lead pencils must never be used for marking aluminium/zinc, and unpainted or pre-painted steel products. The carbon in the pencil promotes corrosion which will etch the surface of the material, leaving a permanent mark. Use a pencil of any colour other than black, a marker pen, or crayon.
Cut pre-painted steel material with care to avoid marring the high-quality finish. Cut by shear only — use nibblers or hand shears. Friction blades and high-speed saw blades must not be used on metal cladding. These blades will damage both the metallic coating and the pre-painted steel surface by creating excessive heat, and generate large amounts of hot swarf which will get embedded into the coating surface
All debris must be swept off the job at the end of each day. Prevention of swarf damage is far easier than its cure. (See 188.8.131.52 Preventing Swarf Damage).