My son wanted to be Kai from Lego Ninjago this year.
The head is made of two foam floral wreaths covered with a camping sleeping mat (super lightweight) and covered by flannel backed satin.. the yellow part is 3 layers of see through fabrics (tulle, organza?, some sort of sheer stuff ). he could see through it easily.
The body is made of foam core and covered with the same red satin.
The legs are made with an oatmeal can cut in half for that wierd lego hip bubble thing in the front and camping pad structure with shoe boxes for feet. I intentionally left the legs a little "high water" so he could walk easier..
Forgive the horrible picture quality - our house was broken into this summer and the jerks stole my digital slr. wah.
It was actually a lot of fun and pretty true to lego scale.