Asbestos roofs are generally made of a corrugated moulded product that is generally fairly stable material. Being a brittle roof there are other significant issues which include the potential of falling through by walking on them.
Roof membranes ar egenerally a bituminous material. They can reside at the tope of the roof or underneath roof tiles in a sheet material. They are usually a black colour and the asbestos fibres can generally be seen with the naked eye.