You can give the value " 0 " for setting unlimited
Syntax for this is as follows
wwwacct <domain> <user> <pass> <quota> <cpmod[advanced/?]> <ip[y/n]> <cgi[y/n]> <frontpage[y/n]> <maxftp> <maxsql> <maxpop> <maxlst> <maxsub> <bwlimit> <hasshell[y]/[n]> <owner> <plan> <maxpark> <maxaddon> <featurelist> <contactemail> <use_registered_nameservers> <language>
for example
/scripts/wwwacct newtest.com new test123 0 y y y 0 0 0 0 0 0
And the features of this domain newtest.com will be as follows
=============
DNS=newtest.com
RS=y
OWNER=root
PLAN=default
CONTACTEMAIL=
CONTACTEMAIL2=
LANG=english
MAXFTP=0
HASCGI=1
MAXSQL=0
MAXPOP=0
MAXLST=0
MAXPARK=0
MAXADDON=0
FEATURELIST=default
MAXSUB=0
=============