My son wanted a Transforming Optimus Prime costume. Don’t they all!?! Anyway…
We started by finding a Powerwheels truck body and re-figuring it. We cut the nose (fenders and hood) from the body (cab) and the bed, then reattached them all so that they hinged. Basically, my son stood inside the cab, which sat on his shoulders. The nose folded down in the front and the bed folded down in the back so that he could walk. The wheels were permanently attached to the body, since they’re normally on axles. We made a body suit for underneath and added a bunch of flames made out of foam to his legs and arms.
We painted the Powerwheels body with the Optimus paint scheme – red fading to yellow, with the blue flames and Transformers logo on the hood. When my son was ready to transform, he would lift the nose up with his hands and push the bed up with his foot and kneel down inside the truck. It sat like a full truck powerwheel with his head sticking out the top.
My husband made an Optimus Prime mask out of foam, painting it silver and blue and layering it. It was light weight, but 3 dimensional. Very cool. The look was completed with his candy box, the Allspark. Great costume and lots of compliments!