Despite chalk being a soft sedimentary rock in real life, Pixelmon's could be made by crafting Diorite with something else (ideally something to 'soften' the Diorite) and give a stack of 16 for each block of Diorite - logic there being blocks are 16 pixels tall and when placed chalk would lie flat like redstone. Placeing it down into the world would use the exact same logic as redstone with it connecting to itself in lines, at right angles, 3 and 4 way intersections, and over increases in height of one block tall.
This was inspired by how some stadiums look in the anime. Do a google image search of "pokemon anime stadiums" to find some examples.