1" tubing is sufficient, alum is also ok if you want to go that route, just understand you'll prob get black on it from the burn/soot. Its all going to depend on what you want to build,... 1 tier, 2 tier, 3 tier? I would suggest measuring for what you want to end up with, but keep in mind how long you think it will take you to get there. I think if you go with anything larger than 1", plan on using casters or just design casters in anyway... its always going to make it easier to move around. Your surface area is going to depend on the size of your burners, but you also need to know what kettles you're going to use, they come in alot of different dimensions so that is also a concideration of how you design it. I guess where I'm going is decide on the equipment you're going to use and then design around that.