Roasting a half pig is commonly associated with a grand get together called a pig roast. A half a pig is a substantial amount of pork, so it is best if you invite your friends and neighbors to help you get through that amount of meat. Otherwise you are resigned to freezing 100 pounds of left overs. Before you can roast your pig you must slaughter and dress it unless you buy your half pig from a butcher shop in which case a good portion of the work is complete.
Set up your pit. There are portable pits and spits and steel pans, but unless you roast professionally or more than twice a year, do not spend the money on a portable pit or spit. A ground pit is traditional and more than sufficient. Dig the pit two feet long and wider than your hog half. Fill the bottom with charcoal and wood, preferably with an aromatic wood like mesquite. Fire the timber and allow it to burn and coal. Add more wood and allow it to burn until it is coals. Add wood until you have eight inches of coals.
Rub the hog half in butter or oil. Be liberal. Oil prevents the hog from drying up and burning. Add spices. Anything you can imagine that might add flavor. Salt for certain, curry, basel, sage, cumin, and cinnamon. Massage the spices into the oil. Wrap the entire half in tin foil. Do not leave any part of your half hog uncovered. Anything you do not cover with tin becomes crispy at the least and will probably burn. Wait for the wood to stop flaming. You only want coals. Drop the pig on the coals and wait two to three hours.
Flip the pig over on your coals. Pull some of the tin foil back and cut into the pig. This is critical. People will eat burnt hog, they will not eat raw pig. Not only does it lack flavor, not only is it tough, eating raw hog is dangerous. If the pig's meat is soft and dark pink, easy to cut and greasy, you are good. If the half hog is fleshy and and meat is whitish, cook the other side for several hours and flip it over again.
Push your hog around in the coals. Laying your hog on top of the coals will probably mean your pig will not roast properly. Push coals up around the hog. If you have an abundance of coals, push the coals as high up on the hog's body as you can. Remember, if your hog is just right on the outside, it is probably undercooked on the inside. The prime meat of a half hog should be on the ribs. If you are perfect everywhere else, you either got your coals just right or your hog is a little raw in the middle.