Thanks for the question about building your website in the background. The option to use a Staging site is a solution that may just fit your exact needs. This option allows you to keep a site active while working on another that people cannot see. When you are done, you can then publish the staging the site taking the place of the live site. You would need to have built the original site in WordPress, though. Check out this article on setting up Staging in BoldGrid for more information.