The roofs of these garages are made from asbestos sheets and if they are deteriorating then they need to be replaced. You will see that from the fact that they are becoming porous. If you need the roofs of these garages replaced, there is no point in replacing them with felt. This will not last and you will end up replacing it again. We can source the correct roofing materials for these garages which will last for years, so please get in touch if you find you have a problem.