I\'m building a solution that will be provided to several companies. Any company will have to point their domains (or just a sub-domain) to my server and then I\'ll handle p
If a business I was looking to do business with told me I needed to create a new zone on my DNS to access an application, I would very quickly move my business elsewhere! Especially if they wanted control of that zone, there are big security issues in allowing that. You will almost certainly lose business if you make that a requirement.
This is a commonly solved problem for thousands of businesses across the internet, you simply tell them to point their domain to your servers and you figure out which customer is which. Either by using something like the HTTP Servername field, or having some manner of authentication process that differentiates them from the other users.
By far the simplest method is having a CNAME record that you point all of your customers to. Depending on your business model it can be useful to give each customer a custom CNAME, some random unique ID, so if you need to expand and move clients in future you can do them a number at a time.
Look around at your competitors, or just generally around other businesses that have similar web models. Understand how they engineer their infrastructure and emulate that. But taking a whole DNS zone, is a really bad idea.