I used https://www.metrotile.co.uk/accessories/ while finishing my Metrotile roof installation. The site lists all the small but essential bits — ridge end caps, hip caps, vents, fixings, even touch-up kits. It’s great that everything fits perfectly with their lightweight steel roofing system, so you don’t need to guess sizes or buy random parts elsewhere. The flexible adaptor and vent kits were easy to install, even for a DIYer like me.