Here is a sample thesis that fits Atticus' character.
Atticus influenced Scout by living a life of examples, instructing his children in moral expectations, and loving her with all his heart.
Write your first body paragraph about how Atticus always showed repsect. We see this with Mrs. Dubose, the Radleys, and even Cal when Aunt Alexandra wants Atticus to get rid of her.
Your second body paragraph should be about Atticus' direct instructions to the kids. He told them not to play the Boo Radley game, and to stop tormenting Boo. He also told her it was not okay to fight or react to people calling him a nigger-lover.
Your final body paragraph should be about the times when Atticus allows Scout to sit on his lap. These nurturing moments (about getting to read together and reading The Gray Ghost in the end) build their relationship in terms of loving engagement with each other.