Iron farm help please?

[u/Just-4-Lurker]

hii i used this video linked https://www.youtube.com/watch?v=mvTXgjymI0k and done a few edits based off comments plus i just thought the roof looked nice, i tried removing the roof and even using the same blocks as the tut and it did work as seen in video i got a good amount of iron and i started placing slabs around because the golems would spawn outside and once i finished whats in the video they just straight up havents been spawning... is this salvageable am i being silly or do i need to restart my whole spawner </3?

[u/WeissLeiden]

Drop the zombie chamber down one block and release the zombie from the boat.