get yourself some trash bags or plastic bags , whatever you might have or like best.

PLEASE NOTE: european plastic bags are different to american or british ones. the ones i used had a much thicker texture then these thin ones you have over in the US.
i figured a 4 layer plastic bag is best
but in an american description says its best to use 8 layers

now, you lay down the plastic between 2 sheets of the baking paper or the wax paper . lay it down flat and just iron over it.
try to set the iron not too hot, so it doesnt burn,wrinkle or does other funny stuff. you WILL mess up a lot but once you figred out the temperature its easy.

now you should have several rather slender pieces of thick plastic that you can bend and use like fabric.
so off to the sewing machine.sew the stripes of plastic togeter and get yourself a pattern, i used this one
if you re not the math talent like me ,its not easy to figure out the measurements, but a little time will do well :D

now, all you need is straps,buckles, and velcro closures, these are expensive in stores, but go out and search for old car seatbeltbuckles and seatbelts. an old backpack might give you its guts , i mean velcros , closures buckles, whatever you migth like.