Step 3: Making it all charlieplex like
The first picture below shows one section (thick lines) with LEDs attached. Each row has LEDs attached to the mesh with the same polarity. The next row is attached with the opposite polarity. Each alternate row is connected together. This forms another charlieplex line.
So for the schematic below if I wanted to light up the top most right hand corner LED I'd put a +ve signal on line C1 and a -ve signal on line C11. The topmost LED in the next mesh would have a +ve signal again on line C1 and a -ve signal on line C12 and so on.
Because I have 5 rows in each mesh I connected the bottom row alternately as shown. A 6x4 or other even numbered mesh would simply repeat the top connection scheme.
The second picture is a rough 3D schematic....which I hope shows the connections with a little more clarity.
The final picture shows a partially completed grid.