How do I pick the right reaction-to-fire class for composite roofing panels on this job?

In Europe, reaction to fire is classified under the Euroclass system, from A1 down to F, often with extra smoke and flaming-droplet sub-classifications. The class you have to hit is driven by the building, so its use, height and where the element sits all feed in. That comes from the fire strategy and building regulations for the project, not from the panel on its own. Two watch-points with composites: a rating applies to a specific tested build-up, so a change of core, facing or thickness can invalidate it, and a single component's class is not the same as a whole-system result. Ask the manufacturer for the classification report and its scope, then check the tested build-up matches what you are installing. Where the required evidence is unclear, get in touch with the build-up and the right testing route can be confirmed.