The bags I have my patterns in are the bags they came in when I purchased them.
If you're talking about patterns like Simplicity and such, I just iron and fold the pattern pieces when I'm done so they slip nice and flat back into the pattern envelopes and I store those in the pattern boxes you can buy at the fabric store.
I ask for the empty bolts at the fabric store too to put fabric on that I have a lot of. The other fabric I fold and group by color and put in my closet.