Go to your bank open up an escrow account and deposit your rent on the 1st of every month. Write a letter to the landlord and have it go certified mail that way you get a signed slip back that he received it. Explain to him to please fix the roof, include pictures if you can of the damage. Do not mention to him the rent is in escrow, simply state he will recieve his rent once the damages are fixed.
the purpose of the escrow account is to show a judge if it came down to it that you have been paying your rent but as a renter too you have the right to live in a home that is free of buckets, water damage and now possible mold.

Hope this helps. I know this is the law in NH so you may want to check in with a real estate lawyer to see if its the same for where you live. Good Luck