Old lead can be an important historic document, there is a long tradition of inscribing into lead.
It is malleable and weathers sympathetically, laid properly it can be virtually maintenance free. Lead is available in codes, which can be selected to suit a particular circumstance. Code 3 means the lead weighs 3lbs per square foot, code 8, weighs 8 lbs per square foot. Labels are colour coded eg green for code 3, red for code 5 etc. While lead seems heavy, as a roofing material its actually lighter than thatch , tiles , slate etc.