In the book The Color Purple, why does Shug give Celie a room in the back of the house?

After Celie leaves her abusive husband, Albert, and goes to live in Memphis with Shug, Shug gives her a large bedroom in the back of the house with a view that looks out over the backyard and a creek. Shug says that she gives Celie this room because Celie is "use[d] to morning sun." Based on Shug's statement, then, it is likely that Celie's bedroom windows face east, the direction from which the sun comes up, and so her room gets a lot of sun first thing in the morning. Shug's room is right across the hall from Celie's new room, but it is in the shade because Shug likes to sleep late. The windows in Shug's room likely face west, then. Shug gives Celie a room that she thinks will be most comfortable for her: Celie gets up early and starts the day while it is young, and the light in her room will allow for this. Further, it keeps Celie right across the hall from Shug, and they've grown used to a certain closeness and intimacy that this arrangement will facilitate.

Shug Avery is in many ways a second protagonist in The Color Purple. Through her connection to Celie, first as Mr.____'s lover and later as an intimate confidant and bedmate to Celie herself, she creates dramatic tension that moves the narrative forward. The reader sees her actions through the lens of Celie's narration but is given to wonder about her fundamental motivations; does she act from a place of sympathy, does she recognize something of herself in Celie? She gives Celie a room to grant her some freedom from an oppressive and abusive relationship and to begin to earn some money of her own. This in turn is the catalyst for a great deal of change in Celie's life as she is eventually reunited with her sister and finds a type of peace with Mr.____.

Celie moved in with Shug after discovering that Mr. had been hiding letters from Celie's sister. Celie was devastated that Mr. had been preventing her from having a relationship with her sister, and this was Celie's breaking point after all the years of Mr.'s abuse, so Celie moved into a room in the back of Shug's house. Celie then had a place of her own where she could start a business and support herself.

Celie healed as she began to have confidence because of her success, and continued to develop a relationship with Shug even though Shug saw other people. Celie was heartbroken to learn that Shug had fallen in love with a young man and held onto the hope that Shug's relationship with him would not last.

Celie has left Mr. Albert because she discovers he has been keeping Nettie's letters from her. Even though Mr. has always been a terrible husband to her, this act of cruelty is the last straw because it deprived her of a relationship with her sister. Celie goes with Shug Avery to Memphis. Celie is still in love with Shug, but Shug is more worldly and cannot commit to one person. She gives Celie a room, so Celie has a place of her own and can work on starting her own business, which she does by making pants. Celie becomes more confident as her business grows and through Shug's affection. She is devastated when Shug explains she has fallen for a younger man in her band, though she predicts it will be a short-term affair.