Pizza ovens have circular floors, and parabolic ceilings that reflect the heat down. Because of the circular floor they provide nicely organized workspace: Since pizza baking is a dynamic process, in which the oven door stays open while you add, turn, and remove your pizzas, you have to keep a fire going in the oven lest it cool. The circular floor allows you to simply keep the fire to one side where the roof slopes down, and have most of the floor area free for pizza.
This oven was built by James Bairey, who runs Forno Bravo, a company that imports some of the best Italian pizza ovens to the US and England. Though he will sell you a ready built oven if you want, he also sells kits of the sort one finds in Italian hardware stores, and assembled this oven from a kit in the course of a day. "I wanted to see how fast I could do it," he says, and while it is true that he is experienced, the instructions that come with the kits are clear (and there is email support), so if you enjoy working with your hands it's not that difficult a project.
Note the storage space for wood under the oven, and the single orange tongue of flame within the oven, which was still fairly cool when the photo was taken.
You'll find much more about putting together a pizza oven, including free plans if you want to work from scratch, and a neat photo gallery, on the Forno Bravo site.