Shouldnt be much different than when you did the two story. Just set your plan view to the first floor level, select roof by footprint if applicable, select your overhang distance and check or uncheck defines slope, select all four walls and then click on the green check mark. Then say yes to attach the walls to the roof. There is a book out called Residential Design using Revit 2012 by SDC publications that is VERY good. Their site is www.SDCpublications.com. It taught me quite a few things.