This is a bit late, but here's a link to a Tumblr post I made on how we constructed our Jiraiya costume:
The head is a modified acrylic globe. We bought the globes off amazon.com (search for Acrylic globe):
The chest was fiberglass over a cardboard form, bondoed to be smooth and with craft foam details.
If you have any further questions, I'll sub to this thread. You can also find me on Facebook.
This was a joint project with my friends, and you can find their FB page here: