The first time I folded it was when I was visiting Chicago. I found a small shop that solf special paper there, and I bought a sheet about 50x70cm that was quite thick. For some unkown reason I folded the Bahamut anyway, knowing it was too thick, and indeed it came out horrible.
The next time I folded it from 45cm tissue foil, and the results can be seen here:
http://photos.yahoo.com/giladzn
And the next time I used 40cm tissue foil, the ugly results can be seen on my page.
If you want to really get a good result, I'd suggest at least 50cm of tissue-foil, and make sure it's a prefect square. Also, you should make the first steps very careful not to allow the paper to "slide".
As a last note, I really really liked this model until I learned how to fold it. I think it's a very tedious model to fold (unlike some of Satoshi Kamiya's other super-complex models).