My Friend Of 20 Years Is Suffering From Paranoia But

Question: My friend of 20 years is suffering from paranoia but allow me to describe him by way of an analogy. There was a man on country walk over taken by a thunderstorm. He found shelter in the welcoming home of a stranger. As he entered there were pots and pans on the floor with water dripping in them from a leaky roof. The man asked the stranger why he didn't fix the roof,, to which the stranger looked at him askance as if he were crazy and replied," Fix the roof? It's raining outside". The man said "I know its raining. I mean fix it when its not." The stranger replied, "Why it don't need fixing then".

This is my dilemma . my friend is over all highly functional even brilliant but when a storm comes the roof leaks it seems essentially sound and house intact. My job has to put the buckets out. So now while overall nothing has changed , the roof is beginning to leak easily and the weather is a constant drizzle.

Any suggesstions

Thank you.
I have actually respected and accepted him entirely as he is, leaky roof and all and I recognize I above all wish to do no harm which my story hopefully illustrates. I also I didn't give you a specific example, but only made an assertion.
He enunciates his fears to me where he believes he is always being followed by unknown strangers. the police etc. These fears are unfounded. We were driving when the engine light went off. He immediately catastrophized the event saying that someone sabotaged the car and that escalated to where everyone in the vicinity was suspect to the point he would follow them with his cellphone in hand taking pictures in an extremely agitated manner, it took me over an hour to calm him down and for him to accept a differential diagnosis , that just maybe the car had a normal defect.
Today he approached an innocent woman in a parked car saying that she had followed him and he went up to her car, knocked on her window and told her he was taking her license plate number etc, If I hadn't intervened the frightened woman would have called the police.
let me know if you need additional examples.

I took a little more time reflecting on your reply and the short answer is yes I believe he enjoys the "delusions" or let's say rather his interpretations.

The "beautiful mind" of the connections he pursues, ( without the imaginary friend in tow)

And those ingrained beliefs of harrassement and pursuit no matter how unfounded are not dislodged by my incomprehension or rebuttal. (I think all pschciatrists should hold a session with their clients as the client drives a car, surely the place where mental health is on fine display)
Nevertheless he doesn't enjoy the consequences which ironically serves to reconfirm and enhance his paranoia. He's agreed to CBT in that I have explained it will help him think clearly when confronted by threats (without me denying the threat) but agreement is not actual follow through.. getting an appointment is the tough part.