As JimF said, you need to do some research and see what will work best for you. Do you want just a smoker, or a smoker\grill combo? Rotisserie, reverse flow, vertical?? There are so many designs, each with their own pros and cons.
Do some internet research and see what will suit your needs best, then you can look at building your own version.
Humphrey's Battle Box;WSM; OTS; DPP Trailer Clone, Wood Fired Double Kettle Pizza Cooker