My grandson, Sean, is Evil Luke Skywalker for Halloween this year. As part of his costume, he's wearing a cape I made for him. I found a long, black, princess-style dressy dress at a thrift shop for $3. I cut it to just below the waist for the body of the cape. The midriff part of the dress, from the waist to the lower armholes, became the hood. The waist ties of the dress came in handy to make a flap for a buttonhole; it closes with a single button at the neck. The cape is big but it will probably last him many years for other costumes. According to photos of Evil Luke Skywalker, the cape is supposed to be large to make Luke look mysterious or menacing.
Here he is wearing the cape at the zoo last week. My Father-in-Law is steadying him on the lion.