As I only needed a few villagers for a small trading hall and an Iron farm, I built this one:
Although I read elsewhere that 3 villagers are needed, it started breeding when I had put 2 cured Zombie villagers in it, and works perfectly with 6 villagers now present.
When I move some of these to a trading hall, how far distant from the breeder must it be for breeding to resume? Sources seem to vary about this from 30 to 80 or so.
Learn something new each day
I put my trading hall about 90 blocks away from the breeder and it seems to be find. My world is more industrial so I just have large tubes going between the buildings to make transportation easier.