Are you looking for something like this?
Steeped 1 lb of lightly roasted rolled oats.
3 lbs sorghum extract
1 lb cooked honey (black)
2 lbs cooked sugar (burnt).
4 oz maltodextrin
1 oz Fuggles
S-04 yeast.
The honey turned black fairly quickly, the sugar (dissolved in water to make simple syrup, of course, probably also added some citric acid) was cooked for quite some time. You could probably use something like D2 candi syrup as well (I used a pound of it in a recent mild ale recipe, and it made that fairly dark). I would say to take some honey or simple syrup and cook it on the stove, and take some taste tests (I just let a drop fall of the spoon onto a plate, and wait until it cools a bit) until you feel it hits the roasty flavor you want.
Coffee can also help, particularly if you want that flavor (though it doesn't seem to make as much color impact as you would expect).