I'm not even sure I'm in the right topic. I need to know how to make an oil drum pig roaster?

You have to cut part of it out allowing room for the pig and placing a sturdy bar across that goes through the pig. The coals go in the bottom and the bar should have a crank to turn the pig every once in a while. Why don't you rent one?

I've welded these up before and they are not easily made by the amateur. The 55 gallon flat grills can be a bit easier to make because it take a lot of weight support to spit roast an entire animal. I'd research blue prints.