My son was 5 and obsessed with “big trucks”. The only thing he wanted to be for Halloween was a Peterbilt. So, I used 3 boxes, painted them. I used tin foil for the chrome, LED push lights for the headlights, dryer vent stacker the exhaust stacks.
He loved his Peterbilt Truck Halloween costume! It was a huge hit with his cousin and all his friends too. Very inexpensive!