I would call/write and set a deadline.

"gee mr home owner, I know that you have been busy with the recent rains, and are working hard to get to the growing list of complaints, and I am throwing mine onto the pile. I have informed you of my leaky ceiling 2x now, and since this is the 3rd, I figure you must be overwhelmed taking care of other issues. I am going to propose a solution for you. If you are unable to take care of this issue by the 1st of the month, I am going to call a roofer, and have someone come inspect it with an estimate. I will be deducting this from my rent. Since I am immune compromised, I am not able to withstand a month long wait to have mold/mildew/water issues addressed. Thanks for your understanding"

I bet that will make him put a wiggle in it. He will not want you deducting fees off the rent, nor will he want a qualified roofing company inspecting his property. They are required to make reports about finding mold situations, and water situations and the health board would force him to fix it. Once mold sets into the wood, its darn hard to get rid of. I would make a pest of myself to get that fixed.

Hang in there. its not fun to take an umbrella to bed.