The instructable by niboras is awesome, to fit my son the dimensions had to be increased.
I changed the materials used also, the entire costume was put together with cardboard, four different colors of duct tape, and some plain white glue. The head was made by cutting several rings out of a heavy cardboard watermelon crate that I got from work. I glued the cardboard rings together in a stack and covered it in blue duct tape.
The torso is a box that was tapered and covered in red, white, and blue duct tape.
I made the shield by welding a handle to the back of a 20 gallon oil barrel lid and wrapping it in duct tape.
My son was very excited with the finished product and he received many compliments on his costume while trick or treating.