Your main decisions
Fascia boards support the roof-edge detail and commonly carry the gutters. Soffits close the underside of the eaves; their ventilation detail must suit the roof.
Choose between suitable timber, uPVC and other specified materials by considering appearance, maintenance and how they meet the existing roof.
Agree gutter profile, colour and downpipe positions alongside the boards. A neat appearance is only part of a working rainwater system.