I rent a unit which has asbestos sidewalls and roof. The landlords solicitors have decreed that I must do no work on these structures. In my lease it is the landlords obligation to maintain the external building. It is 5 years now since I requested on many occasions that the leaking roof was to be mended. It has not been done yet they continue to bill me for the rent in full (plus yearly increments). What are my rights? At which point can I stop paying the rent?

As for the leaking roof. Sounds as if you are in the UK but here in the USA, if you request that something be fixed and landlord does fix it, we can have it fixed, pay the bill and then deduct the amount from the next rent check