What is the right thing to do in a situation with adding subdomains by region?

Question

Domain Name System

There is a website, the customer wanted to attach domains to it by region, let's say you are from Irkutsk and go to irkutsk.google.com. What needs to be done to make these domains appear? Are they paid for all cities? What are the pros and cons of this method. A site with the provision of graduation theses, tests, etc. + there is an online payment for these services. I will be glad to any link in which it is written point by point. what to do in such situations!

Answer 1

I did on Opencart run.
I installed Opencart on the main domain google.com
In the domain panel, I registered irkutsk.google.com without creating a folder for it on the server.
In the admin panel, I specified a new store irkutsk.google.com created a lightweight template for the regions and cloned them.
The only thing was that I had to create categories many times because of SEO mega tags, so that when I go to the page irkutsk.google.com/category/diplome there are mega tags, keywords for this region.
All 63 subdomains were indexed without problems.