I'm currently trying to figure out how to put together a gas permeable SWC using unglazed clay roofing bricks here in Spain.
They come in all sizes — 1.5" x 8" x 16" are the ones I'm looking at for ease of handling. Also dirt cheap! 30 cents apiece at the local home improvement store. Put together 10 and you have a 15 gallon gas permeable container for 3 bucks.
I was thinking of sealing the channels and leaving drip emitters in there, so the evaporative cooling in the summer would not dry out the sides of the "soil" in the SWC and for added thermal mass.
My challenge is figuring out how to glue them together so they're watertight without leaching residue into the SWC reservoir that would be phytotoxic to plants or toxic to humans. Never tried gluing brick of any kind. Anyone glued broken terracotta pots?