Abstract: A device having a pair of rails and a pair of guideline holders is provided. The rails are secured to the underside of the roof overhanging a gable. The rails define a slot within which the guideline holders are received. The guideline holders are slideable within the slot and may be releasably secured to any of a number of positions along the rails. A guideline is threaded within and releasably secured by each of the guideline holders.