Roughly level out an area of ground around two bricks width wider than the size of the flue liner. Select a flue liner that is big enough to accommodate a row of firebricks on the bottom and sides and still have enough room for the fire and baking items. Between 30 to 40 inches long, 15 to 20 inches wide and 10 to 15 inches high is suitable.
Cover the leveled area with a course of bricks, staggering the brick joints. Lay a second course of bricks on top, then a third and fourth, then a course of pavers and finishing with a course of firebricks on top.
Center the flue liner on top of the brick and paver base. Lay firebricks on the floor of the flue liner and line the back and sides. Stack more firebricks around the outside of the flue liner and over the top, leaving the mouth of the flue liner open.
Stack a row of regular bricks around the firebrick insulating layer to complete the demountable oven. Once you lite the fire in the oven, stack a couple of firebricks over the flue liner mouth to keep in the heat. The flue liner will last between six and eight firings before you need to replace it.