A properly laid GRP roof will last for at least 30 years with no measurable deterioration. The deck should be of 18mm exterior plywood or sterling floor and be well fixed to the underlying joists. Typically two men can strip, re-deck, laminate and top coat a roof of about 20m2 in one day. The deck may be a new deck or may be formed over an existing roof. You should ensure that the new deck is laid to adequate falls in order to allow good drainage, so there is no standing water on the roof after completion.