The 248-hour private pilot was on an 861-nautical mile cross-country flight in a single-engine airplane when the engine lost power while in cruise flight at an altitude of 8,500 feet msl. Due to a low cloud cover, the pilot was unable to visually locate the nearest airport; however, he was able to locate a nearby road and he turned towards the road for a possible forced landing. As the pilot proceeded toward the road, he noticed an airport was located off to his left and behind him, so he elected to turn the airplane toward the airport. Due to the strong headwind, the pilot quickly realized that he would not be able to reach the airport. The pilot then made a right hand turn and landed in a field. Prior to touching down, the airplane's left wing collided with a tree and the landing gear collided with a fence before the airplane came to a complete stop. The pilot reported that he did not switch the fuel tanks in flight "which was the result of the engine failing." The pilot added that the fuel gauges were inaccurate and the fuel consumption had to be monitored via a timer. The pilot stated that approximately 5 to 10 minutes prior to the loss of engine power, he told himself that he needed to switch the fuel tanks "soon." In addition, the pilot said that he "went through all the procedures except switching tanks" in an attempt to troubleshoot the power loss.