Here's how I've made my own coffee coolatas, I never really measured anything, just went by taste:

Equal parts brewed flavored coffee (iced) and light cream or milk
Sugar (depending on how sweet you want it)
1/4 tsp vanilla extract (omit if you don't want vanilla, or use one of the concentrated flavors that are made for coffee)

Throw it all in an automatic ice cream maker, turn it on, let it go for fifteen minutes or so and you've got a coolata!

You could also put everything in a blender with ice, but I find the consistency is better if you have an ice cream maker.