One word of caution, be very careful with how your contractor intends to
deal with the edges, abutments, verges, valleys, whatever. A number of
GRP products, such as secret gutters for abutments are available which
ensure you don't get leak problems, far too many try to bodge flashings
without soakers or secret gutters. I had to re-timber a roof because of
lack of attention to detail in this area. Roofing really seems to be a
case of the devil being in the detail.

I can heartily endorse this: I had some good people and some not so good
people working on my tiled roof. The not so good did one side, and the
rain came in, at which point the good pair lifted the tiles and showed
me the crappy soakers that were totally useless. And made some new ones.

The final demise of te old hose was in fact a valley that no one seemed
able to fix. The new house that replaced it has two similar valleys,
with lead going infeasible distances under the tiles and thatch (its
where a tile section now abuts a thatch section: blame the council
planners for wanting it that way).