A trivet elevates the food off the wood stove surface, forming the base of the 'oven.' A pot is placed over the trivet to create the walls of the 'oven.' Pots:  I’ve used different pots for the top of the oven.  I’ve turned our large cast iron pot upside down, but the handle gets in the way and doesn’t let the pot sit as flush with the woodstove, so probably lets some heat escape.  Our Romertopf clay roasting pot (see photo at right) has worked well.  Our enamel roasting pan would probably also work well and would be larger.