HI Kerry,
welcome!
you should go visit other BBQ nut at a local contest and ask around a bunch of questions about the different barbecue rigs.
then figure out what you want to cook and how much food do you want to cook at once? is this going to be only for competition?
I have custom build my rig, but ONLY because I don't have any place to buy one up here and I would have had to pay for traveling cost, taxes at the border, so I had mine made right here in town. I use it for catering work, so I can justify the cost and the size. I certainly would change a few things now that I have used it for 4 years... and the number one thing I would change is have the whole thing build 1/4" thick instead of only the fire box being 1/4" and everything else 1/8" thick which is way more affected by weather in competition.
I keep adding to it, and my next step is a hard roof on it and I should be done.
cheers
Martin