After wasting 2 days i'm still not able to set custom root directory.
What I done so far:
created a vhost.conf file in /var/www/vhosts/system/<domain.tld>/conf and content of vhost.conf are same like http://kb.odin.com/en/5464
and after that this command:
/usr/local/psa/admin/sbin/httpdmng...