A fun project! and the cheapest and quickest way to having your own woodfired pizza oven. Good for renters who can't build their own. 

 as other commenters pointed out, you do need to add sand to the bottom of the oven.  this is so that you can set the pizza stones up and get them level, and also so that there is more thermal mass to hold the heat.  A bag of sand cost $3 at my local hardware store. This  is easy peasy.  

As a response to those complaining that the lip of the oven makes it hard to get the pizzas in and out-- just add more sand!  it is easy to make it so that your pizza stone is level with the opening by adding sand to bring it to this level.  

Also, protip-- I suggest getting a soft wire brush to brush the ashes off of the stone.  it's hard to get them all off the stone using just the little rake thing