Let's get started!
First, I drew a scallop shape on the back side of my fabric. If you don't feel comfortable doing it freehand, look for something in your home to trace. But the nice thing about this project was the scallops did not have to be perfect.
I cut it out and used it as my template to do the rest of them. Here are two all cut out to make one scallop!
Then I placed them facing each other...
It was almost time to sew, but since I did them freehand I held them up to see if they were even and did a little trimming in spots where they were not.
Time to sew! I did a couple back stitches at each end to ensure they would not come apart when turning them inside out.
Here it is all sewn together! Not perfect, but you can't tell once you turn it inside out.
See...one nice scallop!
I ended up making 18 scallops (half red, half green) to cover my mirror above the mantel. As you can see there is an unfinished edge, but it will be taken care of once we sew it on to the ribbon!
I pinned 6 scallops at a time to thin white ribbon. Then I got to sewing! I went very slowly sewing this part to keep it lined up and centered, but do what you're comfortable with! And I took the pins out as I went since they held more securely pinned sideways and not straight up and down.
I left gaps in my banner so there would be room to tape the ribbon up on the sides...but after much rearranging, I ended up cutting them all separate to make hanging a bit easier!
What do you think? Are you going to try it? Keep in mind you could do one long banner to hang across the mantel or down your stair banister? I'm pretty sure my inspiration for this project came from here:

http://tatertotsandjello.com/2011/11/thanksgiving-countdown-bunting-tutorial-and-28-grateful-activities.html
Hers is neat because it has pockets you put activities for the family to do together in! Maybe I could add some pockets to mine and make an advent calendar?? We'll see!