I create the custom folders.
I have 2 folders in the offering from my hosting provider:
database and wwwroot
I create additional folders beneath wwwroot to host each customer's website. The FULL DNN installation (as per the upload instructions from Lee

) is loaded into the customer's folder.
My wwwroot has a default.aspx which has a redirection clause: If there is a request for the custA url, then load the custA landing page in the custA folder beneath wwwroot.
So a request for
www.custa.com > wwwroot/custa/index.htm
TIA,
Sean.