UNTESTED rough draft of a Jones Bar bag pattern. Dimensions are eyeballed from the diagram at WhatBar and assuming 710mm wide bars.

Please let me know if it needs adjusting!

I’ve assumed you want a 1″ webbing ladder around the bag but you can use the labelled points to put webbing or velcro wherever you want. Also assumed you want it 4″ deep but you can just make the gusset shorter.