It could be about a large and majestic rooster. Maybe it's a story of how this giant cock was the king of the farmyard, ruling over all the other chickens. He might have a bright and colorful plumage that made him stand out even more.
Once upon a time, there was a little chick. As it grew, it ate a special kind of magical feed. Day by day, it grew bigger and stronger. Its feathers became more lustrous and its body grew at an astonishing rate. Eventually, it grew into a giant cock, standing tall and proud in the farmyard, crowing to mark its newfound size and strength.
There could be many interpretations of a 'first giant cock story'. It might be a story related to a large rooster in a farm setting, where this rooster was the first of its kind with some extraordinary characteristics. For example, it could be the first rooster in a particular farm to grow to an unusually large size, and there could be a whole story around how it affected the farm life, like scaring the other animals or becoming a sort of local legend among the farmers.
I'm not sure what exactly you mean by 'giant cock story'. If it's about a big cockerel in a fable or a real - life encounter with a large male chicken, that could be interesting. Maybe it could be a story where the rooster was very big and had some heroic deeds in the barnyard, like protecting the hens from a fox.