No you can't do pizza in it per say, due to the large opening, you need to retain as much heat as possible for a pizza oven, which is why they have small openings and smaller smoke stack openings at the base of the stack, which further up opens to a larger space.Additionally you will need to get some thing like a pizza stone as well. The reason why you want to retain the heat is that it cooks the toppings and cheese with a in direct heat source, here you will need either a pizza stone or direct heat source, more often then not you will end up with a burned crust and raw toppings.
Not to say you can't do pizza in it, as I do pizza on a weber, what I do however is to slice toppings extra thin, bake the crust on the weber grid first, with the lid on remove it when it's cooked, turn it over place toppings and place back in the weber.Because you have a lid and can build up the heat you don't have to really turn the pizza base around, but then I don't have to move the heat sources to the side and rely on heat to bake the pizza only and far quicker with a direct source.
Basically what you will need to do is add iron door(retains heat well) and add a crude regulator to the smoke stack to control the temp, basically what is going to happen now with the large opening is cold air is being sucked into the braai and out the smoke stack, removing any heat build up, so you will still need to add a air vents to the door, so it sucks in just enough air to remove smoke.
A large open space like that is less then ideal for any sort of baking with indirect heat source, I also very much dislike that it was plastered inside and outside and painted with enamel. As the enamel starts heating up it releases vapors, same applies to plaster, unless furnace cement is used standard clay bricks work fine.
Braai has already been stuffed up....
