– Sand the surface with fine-grit sandpaper from the bottom to the top of your building. It will remove any rust or dirt accumulated on the surface over time. – Wipe down the surface with a clean rag. If there are any large areas of rust, you may want to apply some steel wool or sandpaper before wiping it down again. – Wash down your metal building with water (or, in some cases, vinegar) until all traces of grime are gone, and then dry it off completely before proceeding. – Apply a coat of paint or stain to protect your metal building’s newly cleaned surface from future wear and tear and corrosion damage!