The plot could involve them starting as rivals. For example, they might be on opposite sides in a battle or competition, but then gradually realize they have more in common than they thought and become friends or even allies.
I really like 'Tim and Cassie: Growing Bonds'. In this fanfic, it starts with them having a bit of a misunderstanding which is really relatable. Then as the story progresses, they start to understand each other better and their friendship evolves into something more. It has some really great dialogue that makes the characters come alive.
Another option is Tumblr. There are often fanfic recs (recommendations) on Tumblr. Some blogs are dedicated to sharing great fanfictions, and you might be able to find some good Tim Drake and Cassie Sandsmark fanfictions through those blogs. Just search for relevant tags like #TimDrake #CassieSandsmark #Fanfiction.
I'm not sure specifically about 'lemon' fanfics as they often involve inappropriate or adult - themed content which is not suitable. However, there are many great fanfics about Tim Drake and Cassie Sandsmark that focus on their relationship in a more appropriate way. You can try searching on fanfic platforms like Archive of Our Own and filter for the Teen and up rating.
One great source could be Archive of Our Own (AO3). There are numerous fanfictions there that focus on the relationship between Jason Todd and Rose Wilson. You can search by the characters' names and filter by tags like 'Romance' or 'Adventure' to find ones that suit your taste.
Archive of Our Own is a great place to start. It has a wide range of fanfics, and you can use the rating and filtering system to exclude any adult - themed stories. You can search specifically for Tim Drake and Cassie Sandsmark, and then select the Teen and up or General Audiences ratings.
You can start by looking on fanfiction websites such as Archive of Our Own (AO3). It has a large collection of fanfictions across various fandoms, and there's a good chance you'll find some great Rose Wilson fanfictions there. Another option is FanFiction.net, which has been around for a long time and has a wide range of stories.
One great Rose Wilson fanfiction could be 'Rose's Redemption'. It might explore her character in a new light, perhaps showing her struggle to break free from her past and find a new purpose. Another interesting one could be 'Rose and the Outlaws', where she teams up with some unlikely allies and they go on adventures together.
When writing their relationship, it's important to show the chemistry. Maybe start with some banter between them. Jason's sarcastic remarks and Rose's sharp comebacks can create an interesting dynamic. Also, consider their different skills. Jason's combat skills and Rose's martial arts abilities could be used in action scenes that also further their relationship, for example, saving each other during a fight.