I've also seen one made out of a 3ft metal culvert. Turn on end, cut a hole big enough in the bottom to to insert wood and stoke a fire, at about 2' put rebarb in one end and out the other to form a grill and then cover with a metal trash can lid.

CAUTION!!! CAUTION!!! CAUTION!!!!
JUST A HEADS UP HERE, do NOT use galvanized metals to cook in, on, it will make u sick as a dog!!! the fumes or whatever you want to call them are bad juju man, now after it all the galvanizing burns off?? never been brave enuff to figure when that may be