This is a easy costume for your dog. :) I noticed there were a couple of nigiri sushi costumes out there, but had never seen one that was a maki roll so I decided to try making one myself.
Step 1: Sushi Roll Dog Costume
First you will need your supplies:
Sherpa Fleece (I have a medium dog so I used 1 yard)
Fabric (I like the backside of faux seude because the shiny side looked right to imitate seaweed)
Thick elastic (I also got 1 yard of this)
Velcro (I use the iron-on kind)
Next fold the fabric into itself until you have a long strip. The width will be the final width of the roll so you want to make it a size that will fit good on your dog. Once I was happy with the width I sewed the two ends together in the center.
Now roll your strip of fleece together into a tight roll and sew the end of the roll to the main part of the roll at the end. It doesn't have to be pretty because it's going to be covered with the "seaweed" anyway.
Next you want to sew the elastic to the bottom of the roll near where the end is.
Now you can sew the "seaweed" fabric on the outside of the roll. I folded over the edges on the sides and just did big stitches into the roll, but you can also hide the stiches in the fold of the fabric if you know how to do that (I did that on the left side of the roll).