Gather your materials togeter
cut one of the pant's legs off
depending on how big you want the flap, cut the first layer down to desired amount.
turn inside out
sew the bottom and/or super glue it (i do both)
once super glue is dry (if you used it) turn it back out right side
now use some good strong saftey pins and secure a strap on (you can use super glue instead) or you could sew them on. (the reason i went with the safety pins is becuase there were clips on the ends of the straps)
make it yours! decorate it!