+1 to buying one from Zpacks since Joe sells the fabric and the tape too.
Using 3M brand #94 solvent/cleaner/prep is supposed to help the tape stick better.
Does Steve Evans (Suluk 46) still have cuben bonding info buried on his website?
Start making them without the reinforcement to see how long they last. Upgrade later, only when necessary, to avoid delaying your start. Expect to learn as you go. Choosing smooth, slick cord may reduce abrasion in the cinch channel.
Someone wrote about using the fibers as a straight line when laying out the shape on the fabric. Using a warm (not hot) iron helped make the fabric keep the folded edge but that may have been for sewing.
backwoodsdaydreamer.com has a stuff sack pattern