Patches or streaks of rust, especially where the iron sheets overlap or around nail holes, are one of the most obvious signs that your roof is beginning to fail. When weight is applied to a portion of roof, such as when someone is walking across it, it could even collapse in extreme circumstances. Further investigation typically reveals that the majority of sheets are in a similar state over the entire roof, even in small, erratic patches of break-through rust, which are a telltale sign of substantial rust damage beneath the surface.