Trigger Help Needed for Map

Trigger Help Needed for Map

I am creating this new map which involves the same idea of survival as Dawn of the Dead 3&4. But I can't seem to figure the ammo trigger, which every Marine unit needs in order to attack an enemy! Any information that could tell me how to set this trigger will be appreciated and a Special Thanks will be included in my new map!!! [/img]

There´s a game named Resident Evil or something like that that is using the same thing that you requested. You can copy from that map and paste to your map(of course with some modifications).