I have now built a number of these bags (in different sizes) for both myself and for Club members. They work very well and can be built in less than a day for very little cost.
The photos below show both my bag and my children's bag in use on the field. One big advantage of a roll up bag is that it can also serve as a very handy work area for on field repairs. No more searching around in the grass for small parts/fittings!
The bags in use. Kites fit across the width and pockets along one end hold line winders, handles etc.
The kite guard dog is optional although this one would probably lick you to death if you tried to steal one! One distinct advantage of nylon/tarp material for the bags is easy clean up of excess 'doggy-drool' ;-)
The materials I have used include coated 'bag weight' nylon (from the discount bin at Wal-Mart) and plastic tarps. The tarps work great, are cheap to obtain and are easy to sew but almost any hard wearing and waterproof material should work fine. You will also need four luggage straps, the type designed to fit around suitcases. These can be bought at 'dollar stores' for a buck each and 'normally' include the snap buckle and an adjuster of some type. Try to ensure that the snap buckle has the female part on the fixed end of the strap as the last batch I bought had the male part attached to the fixed end and I had to cut them off and remake the ends using the female part. For sewing thread I prefer a strong nylon (e.g. #33) or a polyester, do not use cotton or poly-cotton as it will rot. You will also need a sewing machine capable of sewing thick materials as at one stage in construction you will be sewing through five layers of bag material and two layers of webbing strap!
The plans are in a PDF document. Click on the link below to view online or right click on the link and select <Save Target As> to save it to your hard drive for off-line viewing/printing (for Mac users click and hold and select from the pop-up menu). The file includes plans and instructions for bags to fit 4 ft., 5 ft. and 6 ft. long kite sleeves.
Have fun building!