Well, perhaps Harry could use magic to shape the island. He might create a magical forest filled with unique creatures from the wizarding world. He could also build a hidden school on the island to teach magic in his own way, away from the prying eyes of the Ministry of Magic.
Maybe Harry decides to make the island a sanctuary for those who are persecuted in the wizarding world. He uses his skills to create impenetrable wards around the island. He populates it with friendly magical beings like house - elves who are treated fairly. He also builds a library on the island that contains every magical book in existence, so that wizards and witches can come and study without any restrictions.
In the 'Harry Potter makes his own island' fanfiction, he could make an island that has different zones. One zone could be a place where he stores all the powerful magical artifacts he has collected over the years. Another zone could be a peaceful garden where he grows magical plants that have long been extinct in other parts of the wizarding world. And he might have a tower in the center of the island from which he can observe and protect the entire place using his powerful magic.
In this fanfiction, Harry could be forced to create an island due to some kind of dark magic threat in the wizarding world. He uses his knowledge and the help of his friends like Hermione and Ron. They might design the island to have its own unique magical ecosystem. For example, they could create a special type of tree that produces potions - ingredients as its fruits. Harry could also make a school on the island for young witches and wizards who are in danger in the regular wizarding world.
He might have discovered the island during one of his adventures and claimed it as his own. Since there was no one else on the island at the time, and he was the first to set foot on it and recognize its potential, he decided to make it his property.
Hermione could be there. She would be really helpful in planning and organizing the island. For example, she might set up a system for categorizing all the magical knowledge and resources on the island.
Perhaps it's an island with a hidden wizarding school, similar to Hogwarts but with its own distinct features. There might be ancient spells protecting the island, and the architecture could be a blend of different magical styles. Harry could have discovered this island during one of his adventures and decided to make it his own. He might use it as a sanctuary for those in need or as a place to study and preserve rare magic.
Maybe Harry discovers a new and unique magic that only he can perform. This new magic could be the mark he makes. For example, he might find a way to combine different spells in an unprecedented way that gives him an edge in fighting the dark forces.
Maybe Harry, tired of the existing power structures in the wizarding world, starts his own empire. He could start by recruiting those who have been marginalized, like werewolves and half - bloods. He'd then use his fame and skills to establish a new order, one based on equality and true understanding of magic.
Some pure - blood supremacist wizards could be antagonists. They don't like the idea of Harry creating a haven for all kinds of wizards on the island. They might try to sabotage the island's creation or attack it once it's made, fearing that it will disrupt the 'purity' of the wizarding bloodlines.
One possible plot could be that Harry discovers the island is a magical place filled with ancient spells and potions. He might use it as a sanctuary away from the wizarding world's chaos, perhaps to study magic in peace and develop new spells.
In this fanfiction, the island could be a place where Harry's family had some sort of connection in the past. There could be a hidden family legacy there. Harry might find old family artifacts, and through exploring the island, he uncovers more about his family's history and how it ties into the wizarding world as a whole.
Maybe Harry Potter, after all his adventures, decides he needs a peaceful place. He uses his wizarding money to buy an island. He might turn it into a magical sanctuary for magical creatures, away from the prying eyes of Muggles.