I am able to swap reedmaking skills for a pipe bag . I need as large as possible . I have a nice set and shes ready to pump and play , only as I am recovering ok from a train wreck that was my right arm , playing on too small a bag , I am carefull not to do that again for a while . hope to get pics on here soon . thanks tom k . 
you might want to be careful not to make one too big. i did once, not much larger in diameter than the one that came with the set (which had to be replaced) and found it terribly uncomfortable. the slight difference in diameter set my arm just a little higher and i seemed to loose mechanical advantage - using different muscles in the rotation - i guess. it seemed that before my arm fit around the bag better and i was simply sqeezing the bag, but with the larger one i was having to actively push down on the bag with my arm to control the pressure - if that makes any sense.
it was so uncomfortable that my arm was cramping. it amazed me that such a slight difference in diameter - making the bag maybe 10-15% greater in circumferance made such a difference in comfort. and i had to make one closer to the original size.
find one that plays comfortably and measure it.
Try at least not to make main section of the bag too long. I made one that was always hitting the back of the bench when I was playing at sessions, and getting pushed forward. Short and stout is better than long and stout.