In reply to Brendan:
What we used to do in the dockyards was seal the material with a PVA glue mixture to bind the suspension material and reduce the release of the fibres upon removal. This is a bit of an overkill but it would help the cement that the roof is made of if you first primed the surface with a 1:20 PVA wash, let it dry and then paint with an emulsion. This will depend upon the state of the cement surface interior surfaces do not suffer the same weathering but are still affected by the moisture and environmental temperatures. If it crumbles when being treated then the only action is replacement as the binding material is failing. This is not common asbestos cement tends to be a solid and reliable material until played around with. Treat and enjoy.