I make a dark lager that's really good. A friend of mine brews the same recipe (gets the same results) and experimented with adding roasted coffee beans following fermentation. He was adding something like 5 ounces of roasted beans in 5 gallons IIRC. He used Starbucks Pikes Place beans.
It was tremendous. I like coffee, and this, in conjunction w/ the dark lager, was IMO better than something like Founders Sumatra Brown Ale. Yeah, it's a brown ale not a dark lager, but it's really sweet compared to what my friend did.
If I were to do coffee in a beer, I'd be looking at directly adding the beans, given how my friend's beer turned out.