There's a few routes you can take, some being easier than others. You can either go for an iced coffee or an iced cappuccino/latte. For an iced cappucino, technically you'll need to start with a few expressos from an expresso maker. For an iced coffee you'll want to brew a very strong pot of coffee. To either, you'll add a very healthy dose of sugar and then chill. Day of, combine your coffee 'syrup' with a good amount or milk/cream.
That's the hard way.
It'll be a substantial drop in coffee quality, but instant coffee makes a pretty good facsimile of a coolata. Here's my current recipe for an instant coffee syrup.
1 C. water
2 C. sugar
1/2 C. instant coffee
Heat the water and sugar until the sugar is dissolved. Let cool briefly, whisk in coffee. Chill.
When combined with milk/cream, this makes a fairly sweet iced coffee - almost like a drinkable coffee ice cream. That's how most of the iced coffee drinks are these days.
In order to match the richness of the commercial products, you'll definitely want cream. This is all very much to taste, but I would first try a test batch with:
2 T. of syrup
8 oz. (1 cup) of whole milk
2 T. heavy cream
And then adjust from there. You can't add sugar to cold milk, but extra instant coffee (if necessary) should dissolve if you put it in a bottle and give it a good shake.