Are you all grain brewing or extract brewing? Steeping grains? Partial mash?
A little more information would help quite a bit.
However, if you all grain brewing, most of the darker grains won't give you the sugars you need. They add a lot of flavor and color. In addition, to get grains that dark, the roasting temperatures are high enough to deactivete the enzymes.
If using mostly extracts, I'm not a fan of using dark extracts, because you have no idea what grains the manufacturer used to make those dark extracts. When I was extract brewing I used light extracts and steeped grains for flavor and color. All dark extract will give you a dark beer, but you can't guarantee that you'll have a stout.