Basement Finishing - Framing Ledge

Am finishing my basement - have had it water-proofed, put a vapor barrier on the walls, will insulate, etc. The problem I'm running into is in the framing.
I have a ledge that runs around most of my basement (knee-wall/frost wall??). It's 3 feet up and 23" wide.
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How do I frame this? Some ideas I've had involve a single top/bottom plate with the 2X's cut at 45-degree angles - or joined at 90-degree angles. I really don't want to have two top/bottom plates unless I absolutely have to.
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Is this an old house with the basement added? In Michigan it's called a "Michigan Basement." The footings are below the outer wall down 3 or 5 feet below grade depending how far north you are.
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Yeah, exactly. Maryland though.
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I'd use a 2x6 as the bottom plate of the upper wall and construct the lower wall so that its top plate is level with the top of the 2x6. Then run 3/4" x 24" plywood between the walls as a shelf. It will give you storage space --- maybe too much storage space : )
I can't envision how a 45 degree wall could be made to look attractive but I'm not really good at envisioning : (
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I was hoping to do sheetrock - kind of make it look like I meant it to be there. And by that I mean joining the 2X4's together. So the one coming down from the wall would be cut at a 45 degree angle to meet the one running horizontal, etc. etc. Sort of like:
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