I would argue that first and foremost to answer this question you must be aware of the role that New York city plays in this excellent text and how in particular it oppresses Willy and represents the futile way he has spent his entire life chasing a dream that has only brought him unhappiness and despair. Remember that New York city was the financial capital of the USA, and as a result, Miller chose to set this play there, using the setting as a symbol of the materialism and capitalism that destroys and crushes Willy. This is shown literally by the buildings that have gradually towered up over Willy since they bought their house and now oppress him. Note how the stage directions introduce the setting at the very beginning of the play:
Before us is the Salesman's house. We are aware of towering, angular shapes behind it, surround it on all sides. Only the blue light of the sky falls upon the house and forestage; the surrounding area shows an angry glow of orange.
Note the significance of the buildings surrounding the house on all sides, pressing in on Willy and the highly symbolic "angry glow of orange." For Willy, the city encroaches on his space making it impossible to grow anything in his garden, which is of course symbolic of the futility of his job. Similes would therefore have to capture this essence of New York as a place of ugliness that kills the dreams of men and fills them with despair. New York was as oppressive as a rainy day. New York was like the loss of hope. Such similes might be good examples of the kind of figurative language you could devise. Good luck!