Question on using Cold Brewed Coffee to a Porter or a Stout

I've never added Coffee to any of my stouts or porters but i find that others that do are excellent taste. What are the recommended ways to coldbrew coffee? What type of roast should i use? How much should i add for a nice rich flavor without going overboard? Will adding the Coffee to Secondary make a porter Black?

I've used cold-brewed, grounds in boil, and crushed beans in secondary- sometimes just one method in each batch, other times 2 or all 3 methods in a batch. I always find cold-brewed added to secondary or at bottling the best method.
Get a French press or nylon straining bag. Take roughly 6-8 oz. water, bring to boil and allow to cool. This will drive off any O2 or chloromines. Add 3-4 oz of Coarsely ground coffee beans to the water and place in the fridge for 24 hrs. The coffee should be like "sludge"-really thick. Add to keg or bottling bucket or secondary. Usually coffee is very up front for the first month, but tends to mellow and meld.