The problem with adding any sugar to a recipe is that it ferments, so adding maple syrup to your beer won't make it any sweeter. If you want a sweeter beer try making a sweet or milk stout, adding lactose (an unfermentable sugar) will help.
If you don't like the coffee flavor I would avoid roasted barley, so use black patent, chocolate, an/or carafa for color. Some people will tell you that this will make a porter, but there are plenty of current and historical stouts that don't use roasted barley (Sierra Nevada Stout for example).
Here is a (modified) recipe that I did with good results (you can add the lactose to taste at bottling time, .5-1 lbs is the general range you should be looking at):
5 lbs Pale DME
.625 lbs CaraMunich III (any medium-dark crystal would work)
7.5 oz of Carafa 1
7.5 oz of Pale Chocolate
5 oz Black Patent
Adding some chalk or baking soda really helps mellow the bite of dark malts, but if you don't know what your water is like I would skip this.
OG 1.053
Enough hops (I used nugget) at 60 minutes to get to ~20 IBUs.
Ferment around 65 with American Ale yeast (001/1056)
If you really want to use maple syrup, I would go with Grade B (which is more flavorful than the fancy grade A stuff) and add it in the secondary so less of the aromatics gets scrubbed out.
Hope that helps, good luck.
