Hi, i would like some help on repairing flat roofs?

Question:HI,I KNOW I HAVE TO PUT A NEW BOARD ON, BUT IT IS ONLY IN ONE CORNER. CAN I JUST PATCH THE AREA OF FELT, OR DO I HAVE TO RE-FELT THE WHOLE ROOF? WHEN I HAD AN EXTENSION BUILT MANY YEARS AGO THEY LEFT THE MAIN ROOFS DOWNPIPE GOING STRAIGHT ONTO THE NEW ROOF, SO DO I HAVE TO MOVE THAT ALSO? IF I CAN JUST PATCH THE FELT WHAT DO I DO ABOUT THE OVERLAPS, DO I JUST PUT THEM UNDER THE OLD FELT AND SEAL? THIS IS THE FIRST TIME I HAVE USED THIS SITE, AND I HOPE SOMEONE OUT THERE CAN HELP ME. I HOPE TO HEAR FROM YOU SOON, WHOEVER YOU ARE, AND I HOPE THERE IS ENOUGHT INFORMATION FOR YOU TO UNDERSTAND MY NEEDS. CHEERS

Answers:
yeah, just patch the felt like you said, but coat the hell out of the roof with stuff they make to insure it is flexible and watertight. Flat roof can be a hassle.