Legal Obligations - Home Purchase Deficiencies

The roof leaks on home you purchased, the day after move in, causing significant damage. Roof was observed to have deficiencies in the inspection report and a condition to closing the deal were the repairs, per the inspection report, to ensure a waterproof seal and deficiencies corrected. The work was done less than a month before the failure. Insurance will not cover due to poor workmanship. The roofer says the seller told them to do the minimum work, which was just a coating. The seller says the roofer is lying.

Three windows also leak and cause damage to drywall. Seller says this never happened to them, even though they owned the house for 20 years. This was not in the inspection report.

Who is liable?