Any coffee you want. After you cold brew for a period of 18-22 hours, cut it with 2 parts water, or whatever you want. I...need to dig up my recipe. I got it here somewhere.
I like to take the concentrate and cut it with condensed milk, and whole milk.
We cold brew in small batches, using a 1:1 ratio (1 lb coffee to 1 gallon cold water for example). Generally, we use a lighter roast, and brew without a filter for 16 -18 hours overnight. The coffee gets filtered in the morning, and makes a really tasty cold brew.