What a FANTASTIC idea!! The ultimate paper doll. This one would be pretty easy to make too - and could be adapted for any type of costume and for either boy or girl outfits! (Imagine a cowboy with paper doll stetson ... or a favourite doll outfit even!)
Now he wants to be a spider ... The base for this costume is a black shirt, pants and three pairs of black socks stuffed with cotton batting. Safety-pin the sock legs to the shirt's side seams. Then attach the legs to one another and to the shirt's elbows using a needle and clear fishing wire. Tie secure knots to keep the legs in place.