Judging by Google searches, wooden 'nails' for fixing roof tiles are definitely a thing of the past. However almost all the searches I have attempted (in an area I don't know my way around) have only turned up offers to sell metal or plastic 'nails'. The closest I came to anything useful were:
ROOFING from English Heritage, and
Wikipedia has Treenail but those are used differently.
At least a drawing of one at PEG TILES IN SOUTH-EAST ENGLAND from the Society For The Protection Of Ancient Buildings (bottom left on page 3).
So I have searched, but unsuccessfully, for some indication of when wooden pegs ceased to be in common use (replaced by metal ones) for 'fixing' clay tiles (hand-made) for roofs. In particular for southern England (specifically, West Sussex).
Can anyone indicate a date?
I'd guess about the middle of the 19th Century.