I would like to know how I can change default web apache directory. I already changed DocumentRoot in /etc/httpd/conf/httpd.conf and after apache restart web server is still pointing to old location /var/www/html/
What exactly are you trying to accomplish? Because normally you should not change this so I suggest you put the original httpd.conf setting back.
The /var/www/html directory is only used for things like phpmyadmin and webmail.
The user's home directory's are made under /home/user/domains/domain.com/public_html by default.
But maybe if you can explain what you are trying to accomplish or to which default web apache directory you want to change and why, we can might be able to help you better.
I don't want to use this server for hosting websites, this is purely mail server, so I would like to have roundcube as a home directory, so if someone will type IP of my server, roundcube will pop-up.
I would like to know how I can change default web apache directory. I already changed DocumentRoot in /etc/httpd/conf/httpd.conf and after apache restart web server is still pointing to old location /var/www/html/
You should change the docroot in /etc/httpd/conf/extra/httpd-vhosts.conf too, and restart apache after the changes. Please follow http://help.directadmin.com/item.php?id=351, so that CustomBuild wouldn't overwrite the customized docroot for you.