Abstract: A roof structure adjustable support frame system comprising a plurality of joist rails configured to adjust longitudinally; a plurality of side rails configured to adjust longitudinally between the plurality of joist rails; a plurality of corner rail connectors configured to couple a side rail to a joist rail; and a plurality of adjustable joist rail connectors. The plurality of adjustable joist rail connectors comprise a joist rail attachment configured to removably attach to an end of the joist rail, an extension support member extending longitudinally from a first end of the joist rail attachment, a hook assembly configured to move longitudinally along the extension support member and engage a roof joist to couple the joist rail to the joist; and a movable stop configured to secure the hook assembly against the roof joist.