covering material
I once did a consulting job for a guy making things with a "stretch press"
Think that's what he called it.
Basically, he took a big piece of metal (an I-beam sometimes), grabbed it by both ends, pulled like hell with a hydraulic jack 'till it was under tension, then wrapped it around a form (mandrel).
When you released the tension, the piece held its shape.
You'd only need one form to make one rib...

How 'bout one inch aluminum tubing about 6' or 8' long?
Crank out a dozen or so, tie them together in the center with a plate.
Then, maybe have a smaller diameter rim to go around the outside ?
How to fill in the reflector?...
This question has also come up a few times and I've never heard an answer:
...can you cover the dish with aluminum screen wire mesh?
Ya might use self-taping screws with washers?
No, what about pop-rivets?
I'm sure you'd find something better.
But as you say, you could crank out a big dish quickly and accurately.
It wouldn't be too expensive, and could probably be pretty light.
Bending the rib to a parabolic form would be the task.
And the Aussies had plenty of good ideas, so that thread is still a good basis for anyone thinking of following through on this idea.