I used the Pleated Tote pattern by Rebeka Lambert of artsycraftybabe. You can get the free pattern here (Look for the free pattern on the right column).She's also the designer of the Phoebe bag.
I tweaked it a bit to make it my version.
Silver Pleated Shoulder Bag
It has a flap with magnetic button closure.Made lots of pockets, as usual, so that my belongings don't go swimming in the bag!
I didn't use interfacing or batting but added a layer of cotton flannel to give it body. I like it soft and slouchy!