Is the cupola functional? Or can it be made to function? That would be amazingly good for ventilation. Cupola + open up the some of the triangle in the gable ends should net you more than enough ventilation. Really cool windows too!
Two possible configurations, depending on how the roof is built
https://www.backyardchickens.com/threads/coop-modification-recommendations.1517556/#post-25543595
https://www.backyardchickens.com/threads/texas-heat.1540139/page-2#post-25998208
Opening up the triangles at the peak would also...
Mine's "aproned" (not a true predator apron) off for that reason. Not high enough for an adult chicken to get under, but I could definitely lose chicks under my coop if it wasn't securely fenced off.
Can you post a photo of the shed? Generally coops with solid flooring don't "need" aprons, though they can be useful for keeping vermin out if there's any gaps underneath.