Originally Posted by FlippingHades

There have been a few DIY bag-making threads on BF over the last 2 years -- when I made my first DIY bag I started collecting links for bag-making resources (incl. blogs, etc...) here: http://bike.zugster.net/compendium/bag-making-resources. The one that really inspired me was recycled banner golden mean messenger bags (which will find you a bunch more threads if you search for that title).

The "Golden mean" blog entry has a pattern, but as you can see - the basic messenger bag pattern is pretty simple, so it's fairly easy to get into. The very first little bags I ever made I prototyped with newspaper and tape:

Two things I'd specifically suggest doing are: 1) practice practice practice -- get some scrap fabric and make little bags to get a feel for things. 2) Look at any bag you can get your hands on -- turn it inside out, follow the seams, see if you can figure out how it was put together. Nothing beats hands-on research. If you've got some beat up old bag or cheap thrift store thing you can sacrifice, get a seam ripper and take it apart!