How can I build a Multisite from different domains on one host with "Domain Mapping plugin&quot

I have some troubles to create a Multisite with your plugin, Domain Mapping. I would like to connect my Domains, dachwiki.at, dachinfo.at and roofstore.at to my administrative site roofus.at without installing worldpress for each one (if it´s possible). So, each Domain is allready forwarded to my Host roofus.at and I tried to link each one to their subfolder with a .htdoc but it didn´t work. So I tried to install worldpress direct in the public folder, created a new network site but the result was the same. (wrong adress). Do I need a database for each domain? How can I manage this to a simple administrative network, based on different themes and linked among one another?

Thanks for help.
Rene