To make it start up as root, you should put it in one of the rc directories or scripts.
If you're running a SysV-type of system (rc.1, rc.2, etc. directories) put the script in the rc.3 or rc.5 directory (depending on what inittab has the starting level set to).
If you're running a BSD-style system (rc.local file, etc.), then add to the rc.local file the commands necessary to change to the directory and start up tomcat.