Thesis statement guidance with a comparison of Shakespeare's sonnets (18/73)?

I'm having trouble creating a thesis statement, my overall objective is to yze how Shakespeare uses objects and scenes taken from the world of nature as metaphorical vehicles for his themes in "Shall I compare thee to a summer's day?" and "That time of year thou mayst in me behold." I have the basic idea that they distinguish between the perfection and immorality of one person, in comparison to the indefinite aging of another, but I'm unsure on how to really formulate it into an appropriate thesis statement, or if it is even possible with solely that.