Hello And Welcome!
I have designed and created a very simple drawstring bag for covering my various makes, models, and years issued of all folding bikes in my collection. The free directions and how to step-by-step instructions are on one of my Flickr sets:
http://www.flickr.com/photos/world-of-folding-bicycles/sets/72157601331380862/
Please check it out. I can do this project in one sewing session.
http://www.flickr.com/photo_zoom.gne?id=988690181&size=l
See a particular example photo of the completed project for the bike only in actual use.