At about 1245 Eastern time, the airplane overran the runway and impacted a ditch. Visual conditions prevailed. The Private pilot reported no injuries; the airplane was substantially damaged. The pilot subsequently stated that during the downwind leg, he observed the engine oil pressure caution light illuminate. A moment later, the engine lost total power. He declared an emergency to ATC and landed long. The airplane overran the end of the runway and impacted a ditch before coming to a stop.