How can I protect my Iron Farm villagers from lightning?
Based on the information on the wiki, a roof 3 blocks above the villagers, and covering them plus 3 blocks in all directions around them should be enough to prevent lightning from damaging them, as lightning will not be able to target blocks with an overhang, and the overhang is far enough that even if lightning strikes directly next to it, the villagers will be out of range of the damage.