a few years ago I helped an engineer (not the easiest of customers!) to become a robot. I used tomatoe cages (he needed 2, a child would need 1). Turned upside down,push down 2 legs to become shoulders and leave 2 legs sticking in air. Wrap the outside with ironing board fabric (the silver stuff). You could cover it with tagboard first to give it a firmer shape. I opened a circle in the face front and covered it with a black mesh. I used the fabric to make sleeves with a strap attaching across back and front under the cage. Then just embellish with bits and bobs.