What to consider
Battens, counter-battens, underlay, insulation, fixings and accessories each have a function. Ridges, gutters, windows and penetrations connect those layers. Specify compatible products and quantities in the quote, with their installation requirements.
Apply this to your roof
Record your preferences in the roof plan. Final dimensions, product suitability and the complete build-up are assessed for the actual roof; keep the agreed details and manufacturer instructions with your project documents.