Coventry has two roofing populations and the wrong assumption about which you have is expensive.
The older terraces are largely slate on cut timbers, often with valley gutters and shared party details where the terrace runs. Valleys and abutments are where the water gets in, and a valley that has been patched for twenty years will keep failing in the same place until the lead is renewed properly. Sealant does not fix it, it just delays the conversation.
The post-war housing is concrete tile on trussed rafters. The mistake here runs the other way round. A roof built for concrete tile will generally take slate, but a roof built for slate cannot always take concrete tile, because concrete is heavier. If somebody offers to re-cover an old slate roof in concrete without looking at the structure first, get a second opinion.
Re-covering is the point where Building Regulations become involved, because replacing a substantial part of a covering triggers a requirement to look at the insulation. We arrange the inspection for that and see it through to sign off.
Inside a conservation area the covering material is not a free choice, and with eighteen of them in the city this comes up more often here than elsewhere. We check before quoting and we quote what will actually get through. More on coverings, flat roofs and repairs on our roofing page.