While en route the pilot noticed that the engine began "running a little rough." Unable to resolve the rough-running engine, the pilot elected to execute a precautionary landing to a field. During the landing, the pilot attempted to correct for the crosswind gusts, which he estimated were at 10-15 miles per hour. Subsequently, the airplane's landing gear touched down and the airplane nosed over. Postaccident examination of the airplane revealed that the wing struts were bent and the fuselage was buckled.