There is currently a tendency to want to repaint old metal profiled Plastisol colour coated roofing sheets, as it is perceived as better value and less disruption.
When you consider you still need access scaffold, internal safety netting (as most old roofs have fragile roof lights) before you carry out any work then it pays to weigh up the benefits of a new external sheet. With a 20-25 year coating guarantee from the manufacturer and no application issues or weather dependency (i.e. minimum temperatures), it makes sound economic sense to re-sheet.
The photos below are of a re-sheet project we recently completed in Chippenham.