Open DirectAdmin server console and login as root.
[code will appear after you log in or sign up]
You should see message "OK!"
Download file [link will appear after you log in or sign up] to your computer.
Important: Make sure that file name is "siteprobuilder.tar.gz". Rename it if needed.
Login to DirectAdmin with admin user. It is neccessary for admin user to have username "admin".
Go to "Plugin Manager" below:
Install downloaded file by choosing it in "File" field, typing admin password and clicking "Add Plugin" button:
And when confirmation message is displayed... you are ready to go.
You can see appeared builder button in user's account:
Make the plugin visible in a reseller package if it was not set by default.