I think in every Poe story, as in every gothic tale, setting is crucial in establishing the gloomy, threatening and supernatural mood that dominates his fiction. This tale is clearly no exception, but something you might like to think about is how the description of the house mirrors the state of its inhabitants. Consider how the House of Usher is first described to us by the narrator as he sees it:
I looked upon the scene before me--upon the mere house, and the simple landscape features of the domain--upon the bleak walls--upon the vacant eye-like windows--upon a few rank sedges--and upon a few white trunks of decayed trees--with an utter depression of soul which I can compare to no earthly sensation more properly than to the after-dream of the reveller upon opium--the bitter lapse into everyday life--the hideous dropping off of the veil. There was an iciness, a sinking, a sickening of the heart--an unredeemed dreariness of thought which no goading of the imagination could torture into aught of the sublime.
Note how the first contemplation of the House of Usher is inextricably linked with a negative emotional effect on the part of the reader--he describes it as "the bitter lapse into every day life," and he tell us how his heart is impacted with an "iciness." This is the effect of the setting on the narrator, and it foreshadows in a way the state of its two inhabitants and their psychological issues. Living in such a place of unrelieved gloom and depression can only have a negative impact on the characters of Roderick and Madeline. Finally, it is important to note that not only does the setting match the state of Roderick and Madeline, but that also the setting shares their fate, for at the end, the House of Usher is destroyed just as surely as Roderick and Madeline die--symbolising the "Fall" of the line or the "House" of Usher for ever.