I did this cosplay and I really liked this costume. I used this tutorial: http://entropyhouse.com/penwiper/cos...helmsdeep.html
Things I would suggest, when I did this I don't think I bent the armor enough with the heat because I was afraid of ruining it. I also used a curling iron to heat it rather then a stove and I think I should have played with the materials more. If you use the foam, i would suggest buying an extra piece just to mess with to see how far it can bend and be heated.
The other problem I had was the glue. I kept running out so I would buy more than they suggest for the balmung costume because you'll need a lot for it.
The other problem I came across with this was attaching the armor to myself, the leg pieces were easy, I used a sing hole punch to make two small holes for a leather string to fit in (like a shoe lace hole so the strap is under the armor more than outside it. These were easy to hide under the chest piece as well. The piece I had trouble attaching were the shoulders because they were heavier (especially with a piece of a feather boa attached to them). Once I tied them around my shoulders the holes kept tearing and they fell off. I ended up safety pinning them to my shirt that I wore under and making new holes and retying not as tightly. It worked but it was not the most efficient shoulder work.
I do think it's worth trying this because it's a cheaper way and it looks pretty nice when it's finished. I felt my costume looked like metal even though it was foam and was only given away once the pieces broke. I think if you can find a more sturdy way to attach the armor this way could be one of the best for a convention where you're standing a lot.
I haven't tried plastic or metal though and both of those would look even better, but i'm not sure it would be as comfortable with the weight and bulkiness the shoulders have.
I hope this helps and good luck