Concerning your question on Shakespeare's Macbeth, I can't write the perfect thesis statement for you, without knowing what you've turned up with your research, what angle you want to take, etc. And I really don't want to presume to write your thesis for you.
What I can do is give you some ideas and some possible thesis statements, then turn the assignment back over to you.
Gender roles and power are reversed and in flux, or constantly changing, in the play.
The witches end up wheeling a great deal of power, and they are androgynous. Lady Macbeth wants power, but as a female, can't have it. She pleads with the spirits to make her more like a man, but isn't--she can't kill Duncan because he reminds her of her father. Macbeth wants power, but behaves more like a stereotypical female when first attempting to get it: he demonstrates pity and mercy by not wanting to assassinate Duncan, because the king has been a humble and fair ruler.
Lady Macduff, too, is trapped in a gender role, left unprotected by a husband that puts the country's welfare above his family's, neglecting even to take her with him or at least move her to a safe place.
Thus, much concerning gender roles and power is present in the play. Your job is to determine exactly what approach you want to take. The possibilities are numerous. Of course, you want to relate gender and power to how the drama works as a whole. One way to help ensure you do this is to connect your primary subject with a literary device or a type of figurative language.
Here are some possibilities:
- Images of the unnatural reflect the state of gender roles and power in Macbeth.
- The theme of "Fair is foul and foul is fair" reflects (or is reflected by) gender roles and power in Macbeth.
- As androgynous creatures, the witches wield power that reflects both male and female gender roles.
Those are just some examples of the kinds of things you could deal with in your essay.