Unless you can magically sh*t out Cordura and Nylon you are not going to have a fun time making that out of Ripstop cotton!
meh, might just do it, i have nothing to lose this time apart from some shoody trousers which i've never used
I predict a very floppy chest rig then! Maybe try get a hold of some thick cotton canvas,Lifchik and Chicom rigs are made out of those and are viable(Still floppy and a bit sh*t)
Could always double up the ripstop and have a sheet of plastic or something inbetween them to keep the structure.