Buy 7/16 of an inch x 48 inch wood dowels that are as straight as possible. Sand the ends with fine sandpaper to avoid snagging the fabric.
Polyester Organza is a beautiful fabric to use, but I recommend buying a heat cutting tool ($30.00 Creative Textile Tool from www.walnuthollow.com use according to package directions) to finish the edges that you tear (cut into the fabric one inch and tear to get a straight line).
Sew a sleeve for the pole, only slightly loose, but before closing the sleeve sew a bit of velcro (soft side) into the bottom end, then use self-stick velcro (prickly side) on the stick itself. Close the opposite end of the sleeve to prevent pole from going through. The velcro keeps the fabric from flying off. I like to leave about 8 inches of pole out as a handle, this allows ease of flagging in all directions without getting my hand caught in fabric. Most flags using this method will be 40 inches wide (plus the 8 inch stick handle) and as long as the fabric is that you bought, mine are about 4-5 feet long.
I use gold thread for the sewing parts, as it will show and is less expensive than buying 10 different colors if you're making a lot of flags, plus it looks gorgeous!