The pilot stated that during the building process, he determined the unusable fuel amount in the fuel tanks with them uninstalled in the wings, placed on saw horses in a level attitude, but did not take into account wing dihedral, wing incidence, or pitch attitude. With respect to the accident flight he departed with what he thought was an adequate supply of fuel. When the flight was 3 to 4 miles from his destination with the fuel selector positioned to the right tank, the engine quit due to fuel starvation. He repositioned the fuel selector to the left tank which restored engine power and continued towards the destination airport. About 1 minute later the engine quit again; the fuel gauges at that time indicated 1/8 capacity in each tank. He established best glide airspeed and after realizing he was unable to land at the destination airport, he executed a forced landing in a marsh short of the runway. After touchdown the airplane nosed over and although the emergency locator transmitter (ELT) had activated, the wreckage wasn't spotted until an airplane that was landing flew over at 1645. During rescue of the pilot the right wing was cut off but no fuel leakage was reported. Following recovery of the airplane, the left fuel tank which was not breached did not contain any fuel. Additionally, only a teaspoon of fuel was found in the fuel strainer and the carburetor bowl was dry.Advisory Circular (AC) 90-89A, titled, "Amateur-Built Aircraft and Ultralight Flight Test Handbook" dated May 24, 1995, provides guidance in part for determining unusable fuel amount, and the procedures call for placing the airplane at an angle 5 degrees above the highest anticipated climb angle and to disconnect the fuel line to the carburetor. When the fuel flow stops, the amount remaining in the fuel tank is considered as unusable fuel.