So here are some serious variations of the simple "poncho" style top that I copied from somewhere. The first two are from Anthropoligie and the striped one is from Nordstrom. All of the tops are a simple rectangle with a head opening. Fabrics/trims are sewn together to create the rectangle or an opening is left in the side seam for the belt.
Seriously this is like the ancient Greek Ionic chifton. A large rectangle of fabric draped over your body and sewn at the side seams.
Don't over think this and you'll be successful!!