A traditional slated roof would last over 100+ years if contructed properly with sound roof, rafters, trusses, purlins, felt, battens and lead flashings around the chimney stack, valleys and the ridge.

Modern day material used in roofing wouldn't give the same life span, maybe 30 to 70 years.

£8000 for replacing a roof is a good price, considering the price of material and labour. At that price I would imagine they are only felting, battening and tiling.

A builder I know in the village is still reparing roofs from the last storm, every type of roof covering was damaged, the church behind me had the roof damaged, those tile were first laid about 125 years ago,