How much kosher salt should I use on an 11 lb. standing rib roast?

Much more than you would think. 1/4 to 1/2 cup of Kosher Salt will generously cover all surface areas. Even with this much salt, its one of the few items I would still serve some salt on the table with, due to the significant circumference.
When you think its salted enough, salt it some more.

You want to salt and pepper liberally because it's the only place on the roast that you season. I don't measure such things, but my mind's eye tells me 1.5-2 TBS.