In article ,
Bob Mannix wrote:

It rather depends how long you plan staying there! Lead/Zinc are 80/40
years (impossible to say, really, but these are guidelines)

GRP (as your builder and the other poster says) 20-25

Ashphalt say 15-20 (not very common but I was offered this)

Felt 10-15

Any feel for the comparitive prices of these?

Darren