I assume you mean box baffles that extend across the full width of the quilt. There is good info on this if you search this forum and also at several suppliers' sites - with illustrations (thruhiker, sixmoons, etc.
To give you a quick idea, you simply cut rectangles of the fabric you plan to use as the baffles - such as UL noseeum netting - as wide as the shell fabric. Stitch these at intervals to one shell, first. Then start at one end and stitch them to the other shell, one after the other. For bomb-proof, snag-proof seams, fold the shell fabric so the stitching is all on the inside.
If you mean baffles that interrupt the down channels, you are talking another order of difficulty. Do-able, but of questionable utility.