Hi Enzo,
Really depends on how much you wanna spend. You can buy a thin, cheap pit at most big box stores for a couple hundred dollars.
For a bit more money, I'd look at the Old Country line of smokers that are carried by Academy Sports and Outdoors. These are actually pretty well made and heavy gauge pits, for quite a lot less than the premium pit makers get.
If you have the money and want to go first class, there are a number of high end pit makers these days. Just a few of the ones that come to mind: Klose, Shirley Fabrication, Yoder, Horizon, and Lang. There are many more than this that don't immediately come to mind, but this is a short list of highly respected builders that'll get you started.
Red