texasbbqforums.com and bbqpits.com
never use galvanized, welding the crap is bad enough for you.
Pig cookers are normally big, if you intend to cook a whole hog. Whole hogs are normally split down the belly and cooked belly down, legs out and insides to the grill. My current pit isn't big enough to cook a whole hog. My previous pit, which I built sent many young pigs into hungry bellies.
My current pit uses 1/4 steel on the main grill and upright smoker with 1/2 on the fire box. The offset fire box is 20" x 24" pipe, this is one part I'd change since I'm not a big fan of round fire boxes. The main grill is 48" x 24" and the upright smoker on the end is 36" x 24". I'm not fond of the setup, my wife bought it for me as a gift one year. While it is a custom built, not standard cookie cutter model, there are a few things Id do differently had I built it. I gave my previous pit away when I moved closer to her during college years ago. I have learned how to cook on it and tuned it over the years but it doesn't cook like my last one. Make sure to "season" or cure a new pit, its almost like cooking on a cast iron skillet for the first time. I went to the local butcher and asked when he was trimming pork butts. He gave me a call and I picked up 15lbs of pork fat which more than did the job.
I don't use gas and once I get it set I can leave it for several hours without touching it. I use 4 digital thermometers when I cook brisket, two in the meat and two in the grill. I keep them all on high low settings get my fire set and then go to bed. The alarm will go off on the remote if the meat or pit temps fall or rise above the set points. Proper tuning is key, enough draft and the ability to regulate the incoming air. Keep the main grill the same cooking temp across the length of the grill is another key issue. Read those two sites and you will have all the info you want. In the meantime here are some brisket, St. Louis and baby back rib pics to get you motivated.