You can do this any size you would like. What we found easiest since we didn't have a template was another dress and we just fold in half. Then you would trace just like the website says. You should cut two pieces and then lay them inside out and sew all around except the bottom. Next you can hem the bottom of the dress.
Once this is done put it aside so you can make your homemade bias tape. You can get the bias tape make at Joanna's for about 5 dollars. This site shows a detailed how-to on bias tapehttp://www.danamadeit.com/2008/07/technique-understanding-bias-and-making-bias-tape.html.
You can make a slit in the back, hem and add buttons to make it easier to get out but we omitted this step.