I remembered I did a cinder block building before. This was the first building I was making for T&D Feeds. I ended up destroying it over the years with various moves and now don’t have room for the building (it’s across the street from the main store).
I used .250x.250 styrene cut into blocks and glued them up. Made a mold and cast a bunch of wall sections. I bet I still have the mold, although it’s probably pretty worn out and I don’t have any casting resin on hand. And I didn’t really like the connection pieces I tried to make.