Without proper vapor barriers and insulation, cooling a wall or ceiling when the other side has access to the outside air exchange, you'll get condensation. Simple fact...when ANY surface gets below the dew point, and on some of the hot days we've had this year, that dew point has been above 70-degrees, at least where I live - you will get condensation. If that area does not get enough air circulation once it gets above the dew point, the moisture will accumulate rather than dissipate. Mold is pretty much everywhere, and only needs moisture and food to grow.
If the contractor failed to provide proper insulation, vapor barrier, and manage air leakage in the areas he installed, IMHO, he's responsible. Now, I'm not a pro or a lawyer, just providing my opinion.