I made one of these tonight.
I couldn't find a pizza pan locally that wasn't coated...so I started poking around at work for something I could use. I ended up finding an aluminum (LianLi) computer case that was in the junk pile. I took the two removable sides.
Traced out my 11" circle
Cut using a jig saw
Drew my grid on with pencil
Drilled my 1/8 holes and my center hole
I sanded it down to remove any burrs
Fitted my elbow and tubing