Have seen a few of those around over the years.
Always with different mounts & feed arms.
Most have been 8'.
Only once I thought maybe a 10' existed (probably not).
See if there is a seam down the middle where two perforated panels were welded together before fabrication.
I'm going out on a limb, and suggest it was a very nice dish-blank someone made 20+ years ago.
By some top dish company with serious metal fabrication equipment.
It was sold to a few little wanna-be high end dish companies.
They then outfitted it with three legs (mine) or four to hold the feed.
It was mated to all sorts of mounts.
Mine is a dull pewter gray and made of Aluminum.
Some have shown up in black.
They don't really seem to be spun so much as stamped in one piece.
I strongly suggest getting it!
Of course I'm cheap, but I'd give $50.
$100 wouldn't be out of line.
IMO, it's one of top 5% most desirable dishes.