Zipper bags

[demoniavbh.livejournal.com]

I haven't seen any tutorials about how to make a zipper bag, a bag made out enterely of a huge zipper. I don't know if you know what I mean...They're like this

In this case the zipper is one side green and the other side white. It's only a zipper wich you can open and have a large useless zipper, but as soon as you close it, it's a bag, purse...
Once you have made one, it must be pretty easy, but the problem lies in the corners, how to saw there the zippers...

I have a little purse made like this and (if I find it) I could make some pics...I was last week in London and the price of the big bags was 70£, too expensive..so I was wondering if there was any pattern or tutorial or whatever about this.

Thanks a lot!
(Sorry about the explanation, it may be not well understood, but in english I can't do it much better *^_^*)