Begin with the existing substrate, layers and drainage. The choice involves more than the membrane: edges, upstands, penetrations and fastening also matter. Compare proposals with the same scope. Mention plans for insulation, a rooflight or future installations before deciding. Ask for the proposed build-up and warranty conditions in writing, including which existing components will remain.
Start with the existing roof
Ask whether the substrate is dry and stable, which layers are present and how water drains. Those findings help determine whether existing layers can remain and which complete roof system is appropriate.
Compare the connections
Check roof edges, upstands, penetrations and fastening in both proposals. These details are designed differently for bitumen and EPDM systems. A material name or a price per square metre does not describe the complete work.
Include future plans
Mention planned insulation, rooflight replacement or new installations before choosing the covering. The roofer can then consider connections and working space together. Ask for the proposed layers and warranty terms in writing.
Make the comparison fair
Use the same roof area and details in both quotations. Check whether insulation, removal and disposal are included equally. A new surface over retained layers is a different scope from complete renewal.
Read what the warranty covers
Ask who provides the warranty and whether it concerns material, installation or both. Check maintenance conditions and the reporting procedure. A long stated term does not replace a clear description of what is covered.
Record why the system was chosen
A useful decision names the material, substrate preparation, connections and reason for the approach. Keep this with the quotation. If the build-up is unknown, agree an assessment before deciding between complete alternatives.