A molded synthetic polymer based shingle is provided as is a roof made up of underlying and overlying of courses of such shingles. The shingles are generally rigid and are provided with upwardly protruding moisture guards on the upper surfaces of their headlap portions, for guarding against wind-blown moisture entering fastener locations at which fasteners are used to attach shingles to a roof. The moisture guards may be of various configurations and by either completely or incompletely surround the fastener locations. Shields having recesses for receiving moisture guards therein, or other downward projections, may be provided at under surface locations of the shingles in cooperative engagement for further protection against moisture penetration and for facilitating alignment of shingles relative to other shingles.