you've got the right idea, why re-invent the wheel, eh. But seriously, it might end up being more trouble than its worth using someone elses script - you may end up trying to remove parts and add new parts, and that can be a nightmare on other folks scripts.
If I were you i would get detailed requirements of the system and design the database to fit, then build you own PHP code and user interface. It may be a bit of work, but, at least you dont have to hold your hands up to someone elses mistakes.
But if you can't be arsed then why not try looking at:😃
sourceforge
hotscripts