It is best from both a visitor point of view and for Search Engines that your site be completed before going live.
You can insert a snippet of code to keep the Search Engines from indexing the site until it is complete.
How to for users of SiteBuilder desktop version: http://www.homesteadconnection.com/Ti...
For users of Plus
DON'T FORGET TO REMOVE THE CODE when you are ready for the Search Engines to index the site.