Hey fellas im thinking about one thing, it is imposible to make zone in which can come others without my permission, if they come to zone without permission he will die.
Here's a script/ tutorial you could modify the code from: https://sampforum.blast.hk/showthread.php?tid=159429
It's made so non-admins will be killed in a certain area, but like I said before, it can be edited.
The streamer plugin has some cool functions for zones and has a callback (OnPlayerEnterDynamicArea) so u dont need to use a timer that checks if a player is in that area.