Pedro: If you can find a copy of Model Activity Press (UK) January/February 2002 issue of Flying Scale Models, there is a complete how-to article that starts on page 10. The headline is Stop! Stop! Stop! Subhead is "Working drag-chutes for scale jets--get stitching with Chris Golds".
Gives all the details you would need including how to size, sew, fold, pack, and stow in the model. Even gives some detail on how to make the 'chute bay' and the cover doors. Regards.