If you are trying to use your own domain name in your Website Builder site you will need to make sure that you go to your host server set up an A Host record and point your domain to our IP Address 220.127.116.11. After you have done that then you can follow the steps below to setup your website with your domain name.
1) Go to Website Builder list and unpublish (pause icon in action column) site in question
2) Click on edit icon (paper and pencil)
3) Go to Settings page
4) Go to SEO / Social section of Settings page
5) Click Domain Name drop down menu, if not already set to "Use your own domain". Disregard this step if it is
6) Go to Domain Name field below drop down menu and replace current domain with new domain
7) Click Update button
8) You're Done!