If you would like to have a default welcome page for your clients that is automatically placed in the root of their public_html folder when their account is created, simply do the following:
Create your welcome page and save it as "index.html".
In your /home folder, create a folder name "cpanel3-skel" and another folder in that named "public_html". So the location would be /home/yourusername/cpanel3-skel/public_html/
Place the welcome page you created "index.html in the /cpanel-skel3/public_html/ folder. Whenever a new client is created, your index.html welcome page will be automatically copied to your clients "public_html" folder and will become their default page (until they delete it or replace it with their own).