The crate was a great foundation, but I think more modifications are needed. If a coop is too dark inside, the chickens will need to get themselves inside for the night pretty early, because if they wait too long they won't be able to see inside and they could get stuck outside for the night.
Also, without enough ventilation especially on hot days, the coop will become so stuffy they won't want to go inside to lay eggs in the nest box and may end up laying elsewhere. Too little ventilation also creates moisture buildup from chickens breathing and body heat, possibly causing respiratory problems.
