Your thesis statement is usually one sentence that identifies the subject/topic of your essay and discusses the main idea.
In your case, because you mentioned that you want to write about how you relate to Boo Radley, your sentence will need to identify and describe the ways in which you and Boo Radley are alike.
To get started with that, you should first think about and list any similarities that are noticeable between you and Boo Radley. Are you both quiet and loners? Do you both have a tendency to go through life more as a spectator than a participant? What about helping out people in trouble?
Once you've thought about that and figured out what points you want to make, then you should combine those into a thesis statement that states that. You will have to adjust the formality of your statement depending on what type of essay or paragraph you've been assigned to write.
For example, an informal paragraph or essay allows for the use of first person pronouns. So your thesis statement could say something like, "Both Boo Radley and I are quiet loners who are more spectators than participants in our lives." A more formal essay would require a more formal thesis statement without first person pronouns.