I was just wondering if it is possible to register your own domain extension? Or does anyone know how do the domains such as .mobi and .aero come about. Any ideas on how this happens and how much something like this would cost? Thanks 
No, ICANN doesn’t “control all domains”. But they are largely “consulted” if one
wants their extension to be technically “found” in the Domain Name System
(DNS).
Shorthand answer is no, you can’t just create your own domain extension and
let it be broadcast throughout the Internet.
You can’t create your own domain ext but You can purchase a 2-letter domain and create subdomains ex. www.subdomain.uk.com
Ok thanks for your comments