How can I publish my SiteBuilder site under a subdomain / sub directoryIn order to publish your site to a specific directory / subdomain you have to use the PRO version of Sitebuilder. You are not able to do this with the regular SiteBuilder version. If you want to upgrade your SiteBuilder to its professional version, you can purchase the upgrade from your customers' area -> Order Extras section.
In Sitebuilder Pro, you should click on the New site icon near to the upper left corner of SiteBuilder. You will be asked for the directory where this site will be published in future.