Choose the roof build-up, not only the membrane.
Bitumen and EPDM are both used as waterproof roof coverings. Suitability depends on existing layers, roof geometry and the details around edges and penetrations. A simple extension roof has different junctions from one with rooflights and ventilation pipes. Ask what the complete build-up will be and how it connects to the surrounding walls.
Tell us about your situation ↗Drainage and the substrate come first.
Water that remains after rain is a reason to assess falls and outlets. A new membrane does not by itself correct poor drainage or a damp substrate. A proposal should explain whether existing layers will remain, how their condition will be checked and whether local depressions need work. Photographs can help prepare an assessment, but cannot settle these questions on their own.
Plan related work together.
Renewing a covering is a useful moment to discuss insulation and edge details. Added thickness can affect rooflights, thresholds and upstands. Mention solar panels or a proposed roof terrace early, because loading and fixings need separate consideration. Prices based only on floor area omit these variables; this website collects your specification before a quote is discussed.