Hang on, one thing at a time.
Do you have an aftermarket exhaust? If you do, then you MUST declare it, else you run the risk of not being insured. You need to speak to them, normally they'll just charge you a fee like about £80, and off you go. Until you hear from them, like tomorrow morning, do not drive your car. Having a policy cancelled can double your insurance next time around, so it's imperative you get this sorted.
As for the roof tiles, unless you can prove negligence then it's on your head to repair. You may be onto something here actually, four times in four years may be excessive, unless it's in the freak weather we occasionally have once a year then you're stuffed.