Instead of making that structure, I used the various sides as shelves. Each system purchased from Target (they were each in the range of $12-$15) made a little more than one and a half cubes of fully shelved paper cubes. To attach the shelves, I used zip ties. As for the extra corner holders that come with the system, well, it turns out that the cats *love* them. Cat toys for years to come!
All these ideas came from SCS, from Target cubes to zip ties, none of it was original with me.