Alan Scott's ovens are works of art--but they are not efficient, they use about double or triple the wood that an effecient oven would use. They are not designed for pizza--they are bread ovens that do not require the intense heat that pizza does. Sure, you can bake pizza in them, but you'll be using a whole lot of wood to do it. You are much better off going with an oven that is made for pizza and that will allow you to bake bread and other items with a whole lot less wood.
If you are looking at kits to assemble outdoors Earthstone or Mugnani will probably be your best bet. I've had an Earthstone, that was assembled from a kit and moved twice, for 17 years and it works great--it is very effecient. Mugnani ovens are OK for home use, but I do not recommend them for commercial, the quality of their refractory material is not as good. But, for home use, it should work. I have a giant Earthstone in my restaurant and it really kicks butt. I highly recommend the Earthstone from my own personal experience.
And in answer to your question regarding square vs round, for pizza, where you are going to crank the ovens upwards of 850 degrees--round is best for effecient thermodynamics. For bread baking where temperatures rarely go beyond 475 degrees and the heat is indirect, the shape is less important. Effeciency is really important because who wants to pump more cords of wood into an oven than necessary. So, bear this in mind when you research ovens. Both Earthstone and Mugnani have web sites.