Three words, mate: Dark Candi Syrup. D-180 and/or D2 are going to be your best friends. I use 2 lbs in my 3-gallon batches, so if you do 5-gallon batches I'd say use at least 3 lbs. Roasted oats and/or some roasted buckwheat are a great addition as well--I usually use between a half-pound to a pound of grains per gallon wort. My GF stouts are always the biggest crowd-pleasers, they're the closest I've come in flavor to barley-based beers. You can add coffee if you want but I've never found it necessary (also I've never been a coffee drinker). The D-180 will give you plenty of that flavor on its own, in my experience.
The key with roasting the grains is to soak them first--you don't need to malt them, I'm talking about maybe an hour-long soak at most--so that they're wet when you toast them. Stir often, and if you're doing a 5-gallon batch you may need to use two cookie sheets. 375°F-400°F is what I toast at. You want the grains the color of a chocolate brownie, not any darker or the taste will be too sharp. Let them mellow in a paper bag for at least a week, though two or three weeks is better. Then steep them at around 140°F for an hour; don't expect any conversion. If you do it right there should be minimal starch contribution to the wort. After the steep add the candi syrup and whatever other fermentables you want (it doesn't really matter--I've gotten fine results with sorghum syrup as well as rice syrup). You can also add a little bit of molasses if you like, it does add a nice roundness to the flavor.
I usually go for an American-style stout, so I like to use either Columbus or Willamette hops in two additions, but if you want a drier stout, you could cut down the candi syrup a bit, up the roasted grains, and stick to English hops (and only do a first addition).
