I ran into this guy at a Farmers Market and he built his out of 55 gallon drums, refractory cement and HO LPG burners.
He had it going on! The skewers were awesome, the Naan was fantastic with his selection of toppings looked great (I had butter) and he's gotten excellent reviews around here. He told me he got his design off the googletron.
Take a look at the Flickr pics, there are some backyard Tandoors with tiled walls, and his vending rigs. Pretty cool!