Sorry, I ran out of time editing to get the chart lined up. Spaces don't get handled well here.

I'm using cardboard as flooring on the ledges for now. For sheathing of course it would be good to find a supply of 24x22x24 boxes, but for most purposes, that size box would be extremely heavy when filled, so I don't know if they're available. Instead I got boxes whose length plus width equals the length [ie longest side] of the desired box. In this case a 12x12x12 box is ideal. Take 2 of them, open them along the seam, fold over the ends 2" so that you get a 22" side alternating with a 24" side. Tape the pieces together end to end on one joining place. Use duct tape if your rabbit doesn't chew it. If she does, you'll have to use something else, like glue. Tape the flaps together so you have a flat 92" [ie twice 24+22] by 24" piece.

Fasten the 24" ends together. Make the places where the boxes join the opposite corners from the doors. Mark, then cut, door & window holes. Make the door holes just a little bigger than the minimum your rabbit needs to get in. Windows can be just a 1" high by 3" wide slit until she enlarges them. Add the floor covering if you haven't already done so. Slip the cardboard over the grid structure & let your rabbit go at it.

Honey is a bit timid, but it took only a few hours until she'd made a 2nd floor window large enough for her to jump out of.

IMPORTANT If you're putting this in an xpen, the upper ledge should either be against high walls or be as far as possible from the pen's sides.

ONE MORE, I THINK.