As a temporary solution you could literally screw some 2x4s to the wall, and use them to attach the cutout a couple feet from the wall between the new vent hole and the light.
Wont block the air but will block the light.
Bummer about the roof…
This raises an interesting question. How much airflow does window screen block? I’ve spent the last 20 minutes researching and found answers from 50 to 80%. None totally reliable.
Still better than nothing. But I’d think a shade or solid block between the light and window (think “The Simpson”...
Sounds like a good plan.
Like bbread said, see if you can use the cutout to block some of the light.
Be careful with fans. They definitely help airflow, but chicken dust and dander are flammable. It’s good you’re moving it, but a barn proof, sealed motor unit is always a good idea for safety.
If you have to choose between ventilation and blocking light pollution, I’d say take ventilation every time. A little sleep disruption won’t kill birds and you can fix it later (a light block of some kind in front of the cutout) if it becomes a problem. But heat stroke is forever.