This is just supposed to be an addition. We were NOT supposed to give an ending.
Consider the setting of "The Fall of the House of Usher" and how it serves a vital function in creating an eerie, unsettling backdrop to the terrifying action that follows. Setting seems to be so key for any form of gothic literature, and so creating a scary haunted house, with suitable noises to augment that terror, would be a great place to start. Then you need to create a story about the family or people that lived there and made it haunted, with momentos that remain! Good luck!
Perhaps you could insert a passage in which the narrator, who feels much foreboding, decides the turn around and not approach the house of Roderick Usher. Then, there can be some force of the setting--be it the house of some electrical/magnetic force--that pulls him, much like the Lodestone of Coleridge's The Rime of the Ancient Mariner, toward and into this house of doom.
My first idea, as a teacher, was to suggest that you begin with the haunted house- describe it in full.
However, focus on the ongoing deterioration. Just like Poe explains that what once must have looked quite nice is now basically destroyed, explain in your paper what was the cause of all this destruction: A curse, Melancholy, Sadness, you choose.
Once you explain what was the cause of all the deterioration, then go into Gothic/Romanticism narrative and describe each aspect of the deterioration, and form a relatioship to the cause.
For example, if you say that the reason for the deterioration of the house was a curse placed by Usher's great grandparents who once killed someone *(this is just an example)
Now, you explain for instance: Due to the nature of rage of this particular curse, every mirror in the house was unable to form a good image of those who looked upon it, as if the vengeance from those they killed wants for them to see their own sin in their faces.
And you do the same with at least 5 more things in the house, which serves as an addendum, rather than a detour from the story