You can just dig a pit and shovel in some coals. No need to get fancy. Wrap your beast in whatever you have handy, the locals use wet burlap sacks and/or foil to roast goats in, wrap the goat(s), put them in the hole, add a layer of dirt, another layer of coals, and come back at the end of the day and eat. Down in the islands they do the same thing, but with banana leaves as a wrapper and sans the foil. This way you don't lard up your flue. Creosote and lard aren't a good combo to have up the flue. The flames shooting out of your chimney will make it easy for the Fire Dept. to find your house, though.
I haven't been to a goat roast in years. Al goes all them time. That boy is crazy about goats, can't get enough of them.
Another hour and a half until the local pit opens. I may have to saunter over in a bit. Get me a snoot and a couple of trotters to go.