Here is a quick tip — you don’t need to use a domain mapping plugin to have a WordPress Multisite with top-level domains and/or sudomains. WordPress allows you to change a sub-domain to a top level domain once you have added the site:
The only important thing is to set the
something empty an empty string in your
otherwise WordPress will always set it to your network’s
$current_site->domain and you won’t be able to login into any of the other sites.