I have built one out of a 50l keg!!
i originally started this -
http://www.fornobravo.com/forum/f43/beer-keg-oven-6142.html
however it has changed alot since. larger chimney, just 2 house bricks to cook on and no insulation was necessary.
the beauty of my design is it can warm up and be cooking in about 30 mins from lighting the kindling. uses 2 house bricks to rest the pizza on and cooks as good as a "proper" wood fired oven. (trust me I've done the Pepsi challenge and the people tested preferred mine!)
very easy to use, portable, and fits in nicely in the home brewery!!! the perfect addition IMO. also makes a great portable outdoor fireplace.
this is my "pizza keg" as it is now. though no dimensions or details there are photos -
http://lemonrhodes.blogspot.com.au/2012/05...that-could.html
let me know if anyone wants more details. god knows there was a bit of trial and error but since have made them for the whole family. And they are idiot proof to cook with
only prob is you need someone that can weld??
anyone interested i'll post more on it. sorry for long post.