Since the designer hasn't answered yet, I can help a little.

First, I'm venturing that this is a gas fireplace with artificial logs, given the appearance of the logs, the proximity to combustible construction and the absence of a sparkscreen, which would be necessary for a wood burning firepit in most jurisdictions.

There are "kits" for gas firepits, meaning off-the-shelf components, but it generally takes a professional to put everything together safely. Working with gas is dangerous, especially if you are working with propane.

It looks like the firepit base is wrapped in steel and the top is cut stone. It could also be concrete. The finish materials should be able to be found locally, but if not, your local fireplace experts should be able to help you with a project like this.
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Doesn't concrete crack with heat?

It can, but our rule of thumb is to keep the flame at least 6" away, so the risk is low. It would be unusual for a properly designed firepit to have a problem.

Thanks for your prompt reply - I will tell my contractor to keep the gas ring 6" away.