If I were a landlord and I rented a property with a leaky roof, the council would be down on me like a ton of bricks, the way to get their attention is to write to them telling them you will not pay the rent untill they fix the roof. Tell them that the very expensive classic car you store there has been damaged, and you are considering your positon regarding compensation. If you are going to repair the roof yourself, you want a rent free period to compensate you for the cost. Last drum of Chromapol I bought was about £90 but it will do a brilliant job of fixing it. As has been said above, its an old overalls and gloves job, but it can be applied to a wet surface, although you must remove moss/dirt etc. Beware! asbestos is very fragile, and goes through suddenly with no warning whatsoever, porous waterlogged asbestos is even weaker. Use crawling boards or a roof ladder, and move the car outside! Also check that the roof joists have not rotted with the leaks. There may also be implications if you have an accident working on council property without their say so. You are quite within your rights to tell them that unless they repair it within a reasonable time (1 month?) that you will repair it and send them the bill! That is exactly what they would do to you if the situation were reversed. Remember, they are our servants, NOT our masters, even though they would have you believe otherwise.
VIVE LA REVOLUTION!
Phil