Shalom, I have plans to make a clay oven in my house, in which it will be closed, the pots will not have direct contact with it, they will be on another surface inside the oven, in which case I can make a pizza in it or milk products and then kasher it and make something of meat?
There is controversy if there is zeiah (steam) in an oven when it is used, and if it becomes milchig or fleishig as a result. According to those who hold that there is no steam in an oven, you wouldn’t need to kasher it, however the surface that you place the food on would need kashering. If you will make sure to keep separate trays for pizza and meaty foods, this would not be an issue.
According to those who are stringent on this, and hold that an oven does have steam, it would need koshering. The, koshering would not have to be libin chamur, rather libun kal 2500-3000 Celsius. The only issue is that the Ashkenazi minhag is not to kasher between milk and meat (which would only apply according to those who say it needs koshering), especially if you are going to use it regularly for milk and meat. Therefore, according to those poskim it would be best to use a different oven, if you can.
Best wishes on your new oven
Magen Avrohom O:CH 509-11, M:B 509-25, Chelkas Yackov Y:D 23-3, Misores Moshe 1 Y:D 25, Shraga Hameir 4-71(3), Lehoros Nosan 1-34(20), Mbais Levi Y:D pg. 22, Chut Shani (Pesach) 10-4, Shevet Halevi.