My homeowners insurance won't cover the waterdamage done to the roof oon my house due tothe incomplete ,incorrect work done on it which the seller didn't disclose to me at the time of sale. So what can I do about this problem if the seller refuses to have it fixed?

1st - You mentioned an inspector. Was he from the city or an adjustor from the carrier?
2nd - Who's your carrier and where are you located?
3rd - Was the home inspected prior to closing & who paid for the insepction?

Your insurance company may have denied your claim for damages resulting from "wear & tear" (lack of good maintenance), and/or the "repair" to roof occured outside the policy term inception date, usually prior to your date of purchase.

Federal law requires sellers of realty property to disclose any knowledge of pre-existing defects in the structure at the closing of your purchase transaction. The seller may have been convinced the repairs were done properly and they had no knowledge that the roof would leak later on down the road after it was sold to you. You would probably have to prove the seller had prior knowledge of defective workmanship for the federal law to apply. Most lawyers would not charge you for an opinion IF you had no chance of winning a court case against the seller. You should develop more concrete facts in support of your claim and then pose your question to a lawyer in your legal jurisdiction.