There are many signs that you will tell you when you need to replace/repair your existing wall cladding. If the sheets are showing signs of corrosion then the outer coating has deteriorated to the point that the metal is becoming weathered and this can lead to flaking/crumbling of the sheets, compromising the integrity of the walls. If there are obvious signs of holes or missing fixings this can lead to water ingress which in turn can lead to the deterioration of the cladding sheets. Wall cladding is often installed in industrial settings and can often suffer dents and tears due to the nature of the environment and machines operating closely to it, keep an eye out for any obvious damage which could lead to something more significant.