He could use magic to create floating shelves for his books and potions. That would be really cool and also save space in the dorm room.
If Harry is being true to his modest nature, he might not go overboard with the customization. He could focus on making it more comfortable and practical, like adding a warm and cozy rug or some soft cushions for when he's reading.
There was a situation where a gay student in a dorm room was a bit nervous about being himself. His roommate, who was straight, noticed his unease. Instead of being judgmental, the roommate made an effort to create a safe and inclusive environment. They ended up having great conversations about acceptance and diversity, and the gay student felt more comfortable expressing his identity in the dorm room. It shows that understanding can exist even in unexpected places.
Flirtatious conversations could occur. For example, one might compliment the other on their appearance or sense of style. Maybe there would be some light - hearted teasing that has a flirty undertone.
Once, a group of dorm mates decided to have a blindfolded taste - test. They got all kinds of strange and random foods from the cafeteria and took turns blindfolding each other and trying to guess what they were eating. There were some really gross - out moments when someone would think they were eating chocolate pudding but it was actually liver mush. It was hilarious to see everyone's reactions.
There could be a story where a sexy mom comes to the dorm room to surprise her son with his favorite home - cooked meal. She ends up chatting with his roommates and sharing some funny family anecdotes.
Some dorm room horror stories are related to bad smells. Imagine coming back to your dorm and being greeted by a horrible stench that you can't figure out where it's coming from. It could be a rotting piece of food stuck somewhere or a mold problem. There are also stories of getting locked in the bathroom. The door handle breaks, and you're stuck in there until someone comes to rescue you. And then there are those stories about pranks that go too far. For instance, a roommate might put a fake spider in your bed, and if you're arachnophobic, it can be a real nightmare.
One story could be that a girl decorated her boyfriend's dorm room with candles and rose petals all over his bed for his birthday. When he walked in, he was really surprised and they had a very romantic evening.
A plot could be that Harry and Hermione are looking for a way to bring back some of the lost memories of the students who were affected by a powerful forgetfulness charm during a battle. In the Room of Requirement, they find a magical device that can restore memories, but they have to go on a quest within the room to find the power source to activate it. Another idea is that they use the room to train for a magical tournament that's different from the Triwizard Tournament. They face all kinds of magical challenges created by the room itself, and in the process, they grow closer as friends and develop their magical skills even further.
A possible plot for a Harry Potter shower room fanfiction could be that the shower room is haunted by the ghost of a former student who was wronged in that very place. Harry, being the brave one, decides to communicate with the ghost and find out what happened to help it move on. Another idea is that the shower room's water has some special magical properties that start affecting the students' magical abilities in unexpected ways. For example, it makes Neville suddenly able to perform advanced herbology - related spells. And a third idea is that the Marauders once hid a prank - related map in the shower room that Harry discovers, and it leads him on a wild adventure around Hogwarts.
One idea could be a story about the Gryffindor Quidditch team in the locker room before a big match. Maybe there's some friendly banter among the players, like Harry Potter trying to boost the team's morale with a humorous speech. Another could be a story of a new student accidentally stumbling into the Slytherin locker room and the reactions of the Slytherin students.