Abstract: The installation of an air conditioning unit upon a roof having a sloping surface includes providing a framework having a first frame and a second frame which are joined for relative reciprocal movement whereby the framework can be secured to roof and adjusted to provide a horizontal seat for receiving the air conditioning unit thereon. Next provided is a plenum assembly having a first element and second element that are relatively adjustable to be secured to the roof and to the air conditioning unit. Chambers within the plenum assembly conduct air from the air exchange openings in the air conditioning unit to respective openings in the roof defining terminalia of the air conduit system with the respective structure.