Originally Posted by DarthParametric
I think you mean Ralph McQuarrie:
Lucas doesn't come up with designs. He gives some vague overview of the plot and then hands it off to concept artists who actually come up with the design (or in the case of the prequels, they came up with about 20 or so designs and Lucas picked the one he liked).
Yes, you're right! I, actually, got to see Episode III in production with the Hyperspace webcast that they put on every week.