I'll not go into all the details again, as they were described last year. But, one means of creating some nucs is to stick them in a tower above the mother box (and indeed the mother). What are the advantages? Less space. Doesn't use additional floors and roofs or nuc boxes. Some warmth to the nucs on top (can enhance this by fitting mesh over holes in the board separating the boxes). Failed ones are simply fused by removing a divider. When you disassemble the stack the bees ...