Add 2 tbsp. dish-washing soap to water in a 2-gallon bucket. Scrub the patio cover with a scrub brush. Rinse the patio cover with a garden hose. Let the cover dry completely.
Scrape any loose and flaking paint off of the patio cover with a paint scraper.
Attach medium-grit sandpaper to an electric sander. Sand the metal to remove rust and any remaining loose paint. The sanding will also add texture that will help the paint adhere to the metal. Wipe away all sanding dust with a rag.
Brush a thin, even coat of oil-based primer onto the patio cover. Apply enough paint for good coverage but not so much that the paint drips. Let the primer coat dry overnight.
Paint the patio cover with exterior paint that matches your home. Apply two to three thin coats of paint, allowing each coat to dry before applying the next. Multiple thin coats will be more durable than one thick coat.