DURING TAKEOFF, THE AIRCRAFT STRUCK A PILE OF LUMBER THAT WAS 62 FT FROM THE DEPARTURE END OF THE RUNWAY. TWO WITNESSES BELIEVED THAT THE PILOT DID NOT USE ALL OFF THE RUNWAY FOR TAKEOFF. ONE WITNESS ESTIMATED THAT THE PILOT BEGAN THE TAKEOFF ABOUT 150 FT FROM THE APPROACH END. THE PILOT STATED DURING TAKEOFF, HE USED 10 DEGREES OF FLAPS; THE FLIGHT MANUAL RECOMMENDED USING 25 DEGREES FOR A SHORT FIELD TAKEOFF. HE STATED THAT AFTER LIFT-OFF, HE FELT A GUST OF AIR ROCK THE AIRCRAFT AND IT DROPPED. WHEN HE RECOVERED, THE PLANE WAS HEADED TOWARD A BUILDING TO THE RIGHT OF THE RUNWAY CENTERLINE. HE TURNED RIGHT TO AVOID THE BUILDING AND SAID THAT HE HIT SOMETHING. THE MAIN WRECKAGE CAME TO REST ABOUT 165 FT AND 159 DEGREES FROM THE INITIAL IMPACT POINT WITH THE LUMBER. THE TEMPERATURE AND AIRPORT ELEVATION WERE 70 DEGREES FAHRENHEIT AND 773 FT. AN INVESTIGATION REVEALED NO PREIMPACT MALFUNCTION OR FAILURE OF THE AIRCRAFT OR ENGINE.