Shelf under concession window - how deep?

OK, so I'm having Pioneer build my concession window, so far they are awesome to work with!
 
The question is, how deep do i want the serving shelf to be - 12", 14" or 16"? I see a guy on eBay who makes them 16", what do you people use? Does it really matter too much?
Dave

your talking about the outside shelf right ?  i wouldnt want it too big..... give em room to get situated but not enough to hang out on.....
i think anywhere from 12-16 would be fine...... are your customers doing own condiments on the shelf ?

The shelf on my trailer is 12", it's a little shallow, have had a couple of "accidents" with food falling off when I set it out in a hurry.
I would go with 16" if I did another trailer.

Ordered a 12 inch shelf from Challenger Door in Indiana.  Very reasonable. 

LOL geez I'm such a dumb-a**...I meant to say Challenger Door! 
That's who it's coming from. I think I will go bigger than 12", I actually do want somewhere for them to hang out, I'm OK with that. and yes, we're thinking of having condiments out on the shelf for the peeps.

I was thinking of looking into getting a shelf on my trailer there is none there now, I didnt think of it at the time but now I want one it will help keep the people from sticking there heads in the window if I forget to shut it.............I hate it when they do that. I saw where they make the whole window but nothing about the shelf??

If you have a shelf at your window sooner or later some non thinking adult will sit there kid (in a diaper) on it. Which is about the most disgusting thing I have ever seen. But I have watched them do it at events numerous times. No shelf on my trailer thank you.

yea I guess thats true too!lol

Nice - fried diapers! 
 
Well, since we are mainly doing this for catering and not vending, i need a shelf. It will allow me to set up a buffet line right on the side of the trailer - something the Forestry Department likes. That way I can get onto remote places and feed the guys without elaborate setups. I could also do this for backyard parties and such...and no diapers, thank you very much!

We have a small 4' long about 8" deep. Big enough to sit food on, small to keep kids off. Thinking about moving it to the back window and ordering a larger fold down unit for the side window.