My first one is 16" in diameter, and 6" high above the bottom. Subsequent ones I've made using a Weber charcoal grate, which is 13-1/2" in diameter. I make the sides of those about 8" above the bottom. I use a piece of expanded plate that is 3" taller than that to keep the bottom up out of the ashes instead of using feet. I haven't noticed any difference in cooking time or conditions with either size basket. I've never filled one all the way, either. Usually about half full. The longest smoke I've done was about 20 hours, and there was still fuel left.
I'm very intelligent, but I mask it by doing stupid stuff.