A VFR PA 28 PILOT CLBED TO 14000 FT ATTEMPTING TO AVOID UNFORECAST CLOUDS ON HIS ROUTE OF FLT.

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I RECEIVED STANDARD WX BRIEFINGS VIA DUATS FOR MY RTE AT APPROX XA00 AND AGAIN AT XD00. I DID NOT SAVE A COPY OF THE BRIEFING; BY MY INTERP WAS THAT IT WAS TO BE A CAVU DAY ALONG MY ENTIRE RTE WITH THOSE CONDITIONS FORECAST TO CONTINUE UNTIL AT LEAST XK00. MY ACTUAL DEP TIME WAS AS PLANNED AT APPROX XF00; ETE APPROX 1 HR 45 MINS. I CALLED APCH AND OBTAINED VFR FLT FOLLOWING; MY PLANNED ALT WAS 8500 FT MSL. PRIOR TO DEP; I OBSERVED SOME CLOUDS OVER THE MOUNTAINS TO THE NE; BUT I ASSUMED THEY WERE SCATTERED CLOUDS AND I WOULD BE ABLE TO FLY OVER OR UNDER THEM. I DID NOT CHK THE WX AGAIN BEFORE DEPARTING. APCHING THE MOUNTAINS IN THE VICINITY OF ZZZ AT 8500 FT MSL; I OBSERVED WHAT APPEARED TO BE POOR VISIBILITY UNDER THE CLOUDS AND DECIDED TO ATTEMPT TO CLB ABOVE THEM. I HAD NEVER ATTEMPTED TO FLY ABOVE THE CLOUDS BEFORE EXCEPT DURING AN INST TRAINING FLT WITH MY INSTRUCTOR (I AM WORKING ON MY INST RATING BUT HAVE ONLY ACCUMULATED APPROX 5 HRS OF INSTRUCTION). I INFORMED ATC I WAS CLBING TO 10500 FT MSL. WHEN I REACHED THAT ALT; I WAS ABOVE THE CLOUDS AND BASED ON MY EARLIER INCORRECT ASSUMPTIONS I THOUGHT AFTER I CLRED A 'LINE' OF CLOUDS I WOULD BE ABLE TO DSND. HOWEVER; IT BECAME APPARENT THAT THE OVCST WAS SOMEWHAT WIDESPREAD; THE TOPS CONTINUED TO RISE AND I SOON FOUND MYSELF CLBING TO 12500 FT MSL AND DIVERTING NE OF MY PLANNED DIRECT RTE AS THE TOPS APPEARED TO BE LOWER IN THAT DIRECTION. I WAS WARY OF CLBING HIGHER; GIVEN THE OXYGEN REQUIREMENTS; WHICH I WAS AWARE OF -- ASIDE FROM THE REGULATORY ASPECT I WAS CONCERNED ABOUT POSSIBLE EFFECTS OF HYPOXIA AS I HAD NEVER FLOWN ABOVE 10000 FT MSL PREVIOUSLY. HOWEVER; THE CLOUD TOPS CONTINUED TO RISE AND I CONTINUED TO CLB TO 14000 FT MSL. I KNEW I COULD NOT LEGALLY CLB ABOVE THIS ALT SINCE I DID NOT HAVE OXYGEN ON BOARD; AND I WAS APCHING THE SVC CEILING OF MY ACFT IN ANY CASE AND THUS QUICKLY RUNNING OUT OF OPTIONS TO AVOID THE CLOUDS. DURING THIS ENTIRE TIME; I CONTEMPLATED TURNING AROUND BUT I CONTINUED TO ASSUME BETTER CONDITIONS WERE CLOSE AHEAD; AND WAS ALSO CONCERNED THAT CONDITIONS BEHIND ME MAY HAVE WORSENED. FINALLY I MADE A SMART DECISION; TO CONFESS MY DILEMMA TO ATC; WHO SUGGESTED CALLING FLIGHT WATCH. I DID CONTACT FLIGHT WATCH WHO WERE VERY HELPFUL; SUGGESTING CONDITIONS SHOULD BE BETTER AHEAD; TO THE NORTH; OR FAILING THAT; AT OR TO THE WEST OF MY DESTINATION. SHORTLY THEREAFTER; I SAW A LARGE BREAK IN THE CLOUD LAYER AND DESCENDED RAPIDLY THOUGH IT TO 6500 MSL. THE REMAINDER OF THE FLIGHT WAS COMPLETED UNEVENTFULLY. I DO BELIEVE I COMPLIED WITH VFR CLOUD CLEARANCE REQUIREMENTS AT ALL TIMES; ALTHOUGH 1000 FT ABOVE IS DIFFICULT TO JUDGE; AS IS 1 MILE LATERALLY (AS I WAS DESCENDING THROUGH THE HOLE ABOVE 10000 MSL). I AM NOT SURE OF THE EXACT DURATION OF TIME I WAS ABOVE 12500 MSL BUT I MAY HAVE EXCEEDED THE 30 MINUTE REQUIREMENT OF 91.211. IN RETROSPECT; STAYING BELOW THE CLOUDS WOULD HAVE BEEN A MUCH BETTER OPTION. I ALLOWED INCORRECT ASSUMPTIONS ABOUT THE EXTENT OF THE OVERCAST LAYER TO INFLUENCE MY JUDGEMENT; AND FAILED TO CONSIDER TURNING BACK WHEN IT WAS STILL MY BEST OPTION. ON THE POSITIVE SIDE; I DID EVENTUALLY ADMIT MY MISTAKE AND OBTAIN THE ASSISTANCE I NEEDED; AND FLIGHT WATCH AND ATC WERE BOTH HELPFUL IN RESOLVING THE SITUATION WITHOUT INCIDENT.