So basically, I have a stair case that goes down into a basement. However the basement is a square. So how would I make both the staircase and the basement ONE ZONE. Remember the entire thing is shaped like a spatula. Also I cant just draw a huge box around it because then it would overlap other zones. Any help would be appreciated. 

Maybe create a new one and give it the same targetname? Maybe :| I'm not a mapper so just throwing out an idea.

In Radiant, press X to enter Clipper mode. Have your zone selected in the 2D view. Click on 2 points, then press Shift+Enter and it will split the selected zone (or any brush selected). You can then delete/resize/do whatever with the two bits of zone (they have the same key-value pair so don't worry about scripts or anything).

I usually just copy the zone and name it the same, it doesnt matter how many zones you have with the same targetname, it will still do what its suppose to do.

You can copy and paste them around, they will keep the same targetnams. You can also cut them with the clipper and resize them and what not. I can conform both of these work 100%, I've done both in my map and I've had no problems.

Yes do what others have said and also make sure that they line up perfectly so that there are no gaps or overlaps. Snap to grid is helpful here.

Thanks a lot guys for responding so fast. I thought there wasn't a lot of people on right now 

I see you got your answer, but I wanted to add that cutting is my favorite choice. Since when you cut an info_volume, if you change the kvp, it will change it in all the other pieces that were cut from it. If you copy it, you have to change each one yourself, if you decide to change kvps, or maybe you just have a typo in one, which can be very frustrating to troubleshoot.