It could be a sleek, enchanted schooner. With sails that can change color according to the magical energy around it. The ship might have a figurehead that comes to life and gives advice, like a wise old wizard.
Maybe it's a small but very fast cutter. The hull could be made of a special magical wood that is resistant to dark magic attacks. It has hidden compartments where he can store his most precious magical items and potions.
It might be a large galleon - like ship. With multiple decks and rooms filled with all sorts of magical mechanisms. There could be a room on board where he practices his most powerful spells, and the ship itself could be powered by a combination of magic and the wind.
It could be a magical sailing ship. Maybe it has enchanted sails that can catch the wind of magic and sail across different magical realms. Or it could be a small, personal ship that he uses to explore hidden corners of Hogwarts lake.
He could have adventures like exploring uncharted magical islands. Maybe he'd encounter new magical creatures and have to use his wizarding skills to either befriend or fend them off. For example, he might come across a group of mermaids who guard a powerful magical artifact on an island.
Harry Potter could own custom-made wands or enchanted jewelry in fanfics. Also, some stories give him secret diaries or ancient magical tomes with hidden knowledge.
There's also a possibility that it's a Chinese Fireball. These dragons are very beautiful and powerful. In a fanfiction, the author might choose this type of dragon for Harry Potter to own because it would add an element of exoticism and grandeur to the story.
Some of the Hogwarts professors could also assist. Professor Flitwick could use his charms expertise to add special touches to the city - ship, like making the doors open with a unique charm. Professor McGonagall could use her transfiguration skills to transform materials into the needed shapes for the construction. And Neville could also play a role. He has grown into a powerful wizard, and his knowledge of herbology could be used to create a beautiful and functional garden on the city - ship.
There could be lost wizards who got stranded on the ship for some reason. Maybe they were on an expedition and something went wrong.
Well, it could be a magic item shop. Since Harry Potter is from the wizarding world, he might sell things like wands, potions, or magical artifacts in Konoha.
Redemption is also a theme. For example, in some fanfictions where Draco is a main part of a ship, his journey towards redemption while being in a relationship with another character is explored. It adds depth to the story and the relationship.
There could be. In fanfiction, the concept of Harry Potter owning a ship can be explored in many ways. The ship might have magical abilities like being able to teleport within the wizarding world. Some fanfics might focus on how Harry discovers and uses these abilities for his adventures or to help the wizarding community.
His character could develop in terms of leadership. As he is building the ship, he has to take charge and make decisions. This would make him more confident in his leadership abilities.