I just bought 2 pieces of aluminum one was 47"X41" the other was 41"X13". It cost 170.00 I/8 thick smooth finish. I was going to use diamond plate,but I'm going to coat it with Herculiner and didn't want to sand blast it ( I didn't want to put the hood on and still dig sand out of my ears) This way I can sand it.
I tried to buy some non-polished aluminum and it was more expensive than the polished stuff. I like the idea with the foam between the ribs.