What kind of roast??? I really like using apple brines for pork and then on the BBQ. Then again I think anything tastes better on the BBQ

Ok I need a slighty better description of the meat first. Does it have a bone in it. Is it thin or thick.

no bone and pretty goddamn thick

IMO if you're not a cook and don't know what you're doing a slow cooker is the way to go. It's easy and doesn't consume time watching over it while it cooks. Do a search on google and you'll find all the recipes you could want.

Wrap loosely in aluminum foil, with carrot, onion and green peper coarsely chopped.
Add 4 ounces of cheap whisky or better, think Jack Daniels, and 12 ounces of beer..
Seal up almost air tight, and put on the grill for almost an hour over medium/high heat.
Avoid opening the packet as long as you can, to keep the moisture in.

When you open it up to check for done-ness, add more beer if not done, and seal slightly less tightly. This is a good point to add garlic(minced, not powder, please).

Done : no pink remains in the center and the internal temp is over 160F.