I want my map to start when I walk into a certain area, so the zombies don't spawn until they go to the area. How would you do that? It's kinda like a paced intro.

First copy _zombiemode.gsc from raw/maps to your mods/mapname/maps folder. Then search for round_start()
Add this under it:

level waittill("start_rounds");

It will look like this:

round_start()
{
 level waittill("start_rounds");

Then just use this to start the rounds and zombies spawning:

level notify("start_rounds");

You can put that wherever your script for starting the rounds is. I would setup a trigger in my map and use that to start the rounds. 

How would I create a script to start the round with the level notify("start_rounds"); and what should the trigger's KVP's be in radiant?

round_door()
{
round_door = getent("round_door","targetname");
round_door SetCursorHint("HINT_NOICON");
round_door waittill("trigger");
level notify("start_rounds");
}

create a trigger_multiple in radiant and give it the KVPS. targetname round_door

round_door()
{
round_door = getent("round_door","targetname");
round_door SetCursorHint("HINT_NOICON");
round_door waittill("trigger");
level notify("start_rounds");
}

create a trigger_multiple in radiant and give it the KVPS. targetname round_door

I added the script to the bottom of my _zombiemode.gsc and I put the trigger_multiple with the targetname round_door kvp, and nothing happens when I go inside of the trigger.

You know what might be better is to just forget about the notify and just do this:

round_start()
{
	activate_trig = getEntArray ("start_rounds", "targetname"); 
 
	for(i=0;i<activate_trig.size;i++)
	{
		activate_trig[i] waittill ("trigger");
	}

Then just go into radiant and right click and add a trigger_multiple and set it's targetname to start_rounds. That's all you need.   

You know what might be better is to just forget about the notify and just do this:

round_start()
{
	activate_trig = getEntArray ("start_rounds", "targetname"); 
 
	for(i=0;i<activate_trig.size;i++)
	{
		activate_trig[i] waittill ("trigger");
	}

Then just go into radiant and right click and add a trigger_multiple and set it's targetname to start_rounds. That's all you need.   

Yes! It worked! Thanks Whippytrout!

I added the script to the bottom of my _zombiemode.gsc and I put the trigger_multiple with the targetname round_door kvp, and nothing happens when I go inside of the trigger.

You probably didnt thread it then.

Also scripts like that should go in your mapname.gsc not zombiemode

Yes! It worked! Thanks Whippytrout!

No problem. 

You know what might be better is to just forget about the notify and just do this:

round_start()
{
	activate_trig = getEntArray ("start_rounds", "targetname"); 
 
	for(i=0;i<activate_trig.size;i++)
	{
		activate_trig[i] waittill ("trigger");
	}

Then just go into radiant and right click and add a trigger_multiple and set it's targetname to start_rounds. That's all you need.   

if there is more than one trigger placed this method wont work. it will wait for each trigger to be activated one by one.
it might be better to do thezombiekilla6's idea mixed with yours.
either, use getEnt or have a separate method that is threaded on each trigger