Good airflow is crucial to prevent mold.
New houses that are built with zero airflow when the electricity is off are a mold magnet when they are foreclosed, simply because the air flow is prevented. Airflow in the attic can be handled with having your contractor install a simple ridge vent in the soffit.
Humidity also must be controlled in the house. Depending on the temperature and relative humidity, moisture can condense inside the walls if the humidity level is allowed to rise too high. This is less crucial in arid states but in humid states on the coastline or in the south, it is a real problem.