try running it like this:
sh -x build update
and see what line it is hung on. Did you install/update your firewall, perhaps it is hung trying to access one of the web servers.
+ ADDITPHP=4
++ grep php5_cgi /usr/local/directadmin/custombuild/options.conf
++ cut -d= -f2
+ DEFPHP_CGI=no
+ DACONF_APACHE_VER=1.3
+ '[' -e /usr/local/directadmin/conf/directadmin.conf ']'
++ grep '^apache_ver=' /usr/local/directadmin/conf/directadmin.conf
++ cut -d= -f2
+ DACONF_APACHE_VER=2.0
+ '[' yes = yes ']'
+ wget http://files1.directadmin.com/services/custombuild/versions.txt -O /usr/local/directadmin/custombuild/versions.txt
[root@reverse custombuild]#wget http://files1.directadmin.com/services/custombuild/versions.txt
--2012-03-26 10:17:31-- http://files1.directadmin.com/services/custombuild/versions.txt
Resolving files1.directadmin.com... 216.144.254.90
Connecting to files1.directadmin.com|216.144.254.90|:80...
Yes that means your wget is blocking. I am guessing that perhaps a firewall is blocking access. I would assume that after a certain amount of time it should time-out and move onto the next step. How long have you let the script run? Please check your firewall, and make sure you are not blocking port 80 ingress/incoming (in this case).