THE ENG WAS REPORTED TO BE SPUTTERING DURING THE TAKEOFF ROLL. THE PLT CONTINUED THE TAKEOFF AND AFTER LIFTOFF DECLARED AN EMERGENCY. AS THE ACFT TURNED TO A DOWNWIND POSITION AT A LOW ALT WITH THE ENG STILL SPUTTERING IT STRUCK A TREE AND A BUILDING AT WHICH TIME A FIRE ERRUPTED. POST CRASH EXAMINATION REVEALED BOTH FUEL CAPS TO HAVE DETERIORATED SEALS AND EVIDENCE OF THEM HAVING LEAKED WATER INTO THE FILLER NECKS. THE FUEL STRAINER AND FUEL FLOW DIVIDER HAD EVIDENCE OF CORROSION DAMAGE. WATER WAS FOUND IN A FUEL LINE FROM THE LEFT RESERVOIR TANK TO THE FUEL SELECTOR VALVE. THE ACFT HAD AN EMERGENCY 3 DAYS BEFORE THIS ACCIDENT WHEN ENGINE POWER WAS LOST AFTER TAKEOFF. SUBSTANTIAL AMOUNTS OF WATER WERE DRAINED FROM THE ACFT AFTER THIS INCIDENT. ACFT RECORDS REVEALED THE ACFT HAD ONLY FLOWN 2 HOURS IN THE PREVIOUS 8 MONTHS. 3 DAYS PRIOR TO THE ACCIDENT THE ACFT WAS FOUND TO ONLY HAVE 1/4 FULL FUEL TANKS AND WAS TOPPED OFF AT THIS TIME. THE ACFT HAD NOT HAD AN ANNUAL INSP FOR 2 YEARS.