I agree with Jon, the puppet will be too heavy, I am afraid. Try to calculate the weight it will have. May be a wooden or aluminium skeleton and carved blocks or foam or expanded polyurethane covered with papier mache could work well. I am just guessing, since I have never work with so big sizes.
Have a look here
http://www.gis.net/~puppetco/ You can get some ideas.
http://www.latiendita.info/escenografia.htm A Spanish site, but you can see big size, carved foam characters