website builder

Hi all
I want to create a Website to provide a user with a chance to design
and generate their own website.Users will have the option to create a
template from scratch or choose from a number of pre-designed templates
which I will have designed myself, and then be able to download it on
to their browser within a matter of minutes. The site will guide the
user step-by-step through the design process, selecting colours, images
etc. Also will help users that already have websites to give their own
website a more professional, updated look.
Anybody have any ideas as to a good editor to get me started or links
that might help?
Going to do most coding in ASP.NET, C# and will also be using
dreamweaver for webpages. any feedback is much appreciated