First make sure you know your mysql root password, you have to replace DATABASEPASSWORD to your mysql root password.
If you have already used RoundCube installation please make sure you remove any traces of it with:

# cd /usr/local/cpanel/base
# rm -rf roundcube*
# mysql -p -e ‘drop database roundcube’;

You will have to specify your root password when prompted.

Now lets download roundcube first and chmod the directories

# cd /usr/local/cpanel/base
# wget -O roundcube.tar.gz http://easynews.dl.sourceforge.net/sourceforge/roundcubemail/roundcubemail-0.1beta2.1.tar.gz
# tar -zxvf roundcube.tar.gz
# rm -rf roundcube.tar.gz
# mv -f roundcubemail-0.1beta2 roundcube
# cd roundcube
# chmod -R 777 temp
# chmod -R 777 logs

Create the database and install the intial sql file. The following commands will do this for you:

mysql -e “CREATE DATABASE roundcube;” -pDATABASEPASSWORD
mysql -e “use roundcube; source SQL/mysql.initial.sql;” -pDATABASEPASSWORD

Now lets sort out the configuration:

# cd config
# mv db.inc.php.dist db.inc.php
# mv main.inc.php.dist main.inc.php

Now open db.inc.php

# nano -w db.inc.php

Find:
$rcmail_config['db_dsnw'] = 'mysql://roundcube:pass@localhost/roundcubemail';

Replace with:
$rcmail_config['db_dsnw'] = 'mysql://root:DATABASEPASSWORD@localhost/roundcube';

Now Open main.inc.php

# nano -w main.inc.php

Find:
$rcmail_config['default_host'] = '';

Replace with:
$rcmail_config['default_host'] = 'localhost';

Now we have to configure cPanel to show roundcube in the theme.
Please note this is for the X theme(default) only!!
If you use another theme please skip the next part and see below.

# cd /usr/local/cpanel/base/roundcube/skins/default/images/
# cp roundcube_logo.png /usr/local/cpanel/base/frontend/x/images/roundcube_logo.png
# cp roundcube_logo.png /usr/local/cpanel/base/webmail/x/images/roundcube_logo.png
# wget http://www.yourserverguide.com/Files/HGpatch-roundcube-1.0BETA2.1
# patch -p0 < HGpatch-roundcube-1.0BETA2.1

**NOTE** If you receive a message stating:
Reversed (or previously applied) patch detected! Assume -R?
Please press N for No as this is because you previously installed roundcube

This will auto do all the necessary changes to roundcube and the X theme.
Once the patch is executed you may now access roundcube via http://yourserverip/webmail

If you do not use the X theme please do the following:

# wget www.yourserverguide.com/Files/HGpatch-roundcube-NON-X-1.0BETA2.1
# patch -p0 < HGpatch-roundcube-NON-X-1.0BETA2.1

Then open your webmaillogin.html, please replace YOURTHEME with the name of your theme.

# nano -w /usr/local/cpanel/base/frontend/YOURTHEME/webmaillogin.html

Find:

</td>
</cpanelif>
</cpanelfeature>

Add Below:

<td align="center" valign="bottom" width="200">
<a href="/roundcube/index.php"><img src="images/roundcube_logo.png" border="0"></a>
<a href="/roundcube/index.php">RoundCube</a>
</td>

Remember to chattr +i the files or add the patch to your /scripts/upcp :

# chattr +i /usr/local/cpanel/base/frontend/x/webmaillogin.html
# chattr +i /usr/local/cpanel/base/webmaillogin.cgi

That’s it! You may now access roundcube via http://yourserverip/webmail