Iron Farm - Door Placement

I've been working on an iron farm in a survival world. I'm on 1.12 Prerelease 5.

I was following this tutorial:

It seems to work in 1.12, because Mumbo Jumbo built the same design on the Hermitcraft server.

It hasn't spawned any iron golems yet, and I have some doubts because this is the first iron farm I've built. I've looked over the wiki, and I want to make sure that I placed the doors correctly. Some of my friends are saying that there need to be transparent blocks above the doors.

So, all in all, I just want confirmation that I'm building the doors correctly. Thanks for all your help!

View of one spawning level:

Doors:

Top spawning level:

Ten villagers right beside the farm:

Killing chamber:

Thanks!

Sky access!

For door to count as village door, it needs more sky above on the outside than on the inside.

You buried your farm under the sand. It can't spawn golems because the doors don't "see" any sky on the outside of the farm. You'll need to dig a trench around the farm (at least in front of the doors, the corners may remain filled) so that the doors have a little sky on the "outside".

Even 1-wide trench, anywhere within 5 blocks away from the door will suffice; it doesn't even need direct "line of sight" to the door (space between the trench and the door may be buried). With the inside of the farm full covered and larger than 4 blocks, what matters is that within 5 blocks ahead of every door, at least one block (upper or lower) is empty and open to the sky.

(don't forget to cover the villagers; zombies would love to drop from above.)