why he chooses to rent the apartment. He has already committed "thoughtcrime" numerous times by writing in his journal, and Winston knows that he cannot appear completely orthodox at all times. Overall, Winston decides to rent the apartment above Mr. Charrington's antique shop regardless of the consequences, because he has nothing to lose and desperately needs the privacy in order to carry out his affair with Julia.

Think of it this way:  Imagine having lived Winston's life.  It was completely and totally miserable.  He grew up starving, lost his mother and sister and blamed himself for it, worked a thankless job doing immoral truth-shifting for an oppressive and cruel government, had a thankless marriage to a cold woman who did not love him or enjoy intimacy, and had nothing to look forward to each day.  Then, in comes Julia, who feels the same hatred for the Party that he does, that enlivens him, loves him, enjoys being close to him, and injects him with new life and vigor.  All of a sudden, there is something worth living for--a person worth living for, and a cause (rebelling against the Party) worth living for.  For the first time in his life, Winston feels alive, and looks forward to getting up each morning.

Now, if you look at it that way, renting the room allowed Winston to have joy in his life.  It allowed him to actually feel like life was worth living.  Julia, used to rebelling against the Party and taking risks, was right there with him.  It WAS a huge risk, but they didn't care.  They were going to probably die anyway, someday, caught for thoughcrime or some other minor transgression, so why not live life to its fullest while they could?  They had this chance to have a bit of brightness in a very bleak world--that is almost impossible to resist, even if it is risky.  It's hard to begrudge them that little piece of heaven, a haven from their repressed and miserable lives.  I hope that those thoughts help a bit; good luck!

In 1984, Winston thinks about renting the room above Mr Charrington's shop because of the difficulties that he and Julia experience in trying to have a relationship. Specifically, Winston wants to enjoy their time together and for them to behave (in public) like any other couple, as he says in Part Two, Chapter Four:

He wished that he were walking through the streets with her just as they were doing now but openly and without fear, talking of trivialities and buying odds and ends for the household. 

In addition, the idea of renting Mr Charrington's room comes to Winston because he does not want to feel as though they must only ever use their time make love:

He wished above all that they had some place where they could be alone together without feeling the obligation to make love every time they met.

These feelings arise as a result of the Party's control over the intimate lives of its members. Under the Party's rules, for example, Winston and Julia's relationship is forbidden and this forces them to meet in secret and only when they have the free time to do so. It is this control, then, which also prompts Winston to think about renting the room. 

In this totalitarian society, any expression of individuality or the merest hint of anyone leading a life of their own is considered deeply subversive. Winston Smith, as a cog in the government machine, is all too aware of this. But having fallen in love with Julia, he's prepared to take the risk. Love does strange things to people, but it's also the ultimate expression of what it means to be human. And in such a society, in which people are radically dehumanized by a totalitarian regime, that's especially important.

Winston rents out the room above Mr. Charrington's shop for the express purpose of conducting his illicit affair with Julia. It provides for both of them a haven of relative peace and privacy away from the daily grind of state-enforced conformity. It's also a place of freedom, a rare and precious commodity at the best of times, but especially so in a society in which everyone is constantly under the watchful gaze of the Party. That little room comes to symbolize the triumph of the human spirit in the midst of systemic repression.

Winston decides to rent this room because he wants a place to stay where he will be out from under the eyes of the Party.  He thinks the room over the shop will give him such a place.

He also feels nostalgic about the room.  It reminds him of better times, times before things got to be the way they are now.  He felt that it was the sort of room in which you could actually be alone with your thoughts.

So Winston takes the room because it reminds him of the past -- of a time when a person could actually be alone.  This makes sense because what he is trying to do by rebelling is to go back to a time when people could think for themselves and be who they wanted to be.

It is no mere coincidence that the main character is named Winston, name of a famously heroic historical British figure who epitomized independence, strength of character, a certain rebelliousness: "Never, never, never surrender!" Indeed, Winston of 1984 refuses to surrender his humanity to the Thought Police. He desires, above all, to be a man--to feel like a man, to think like a man, to live like a man. 

Winston's heroism is "heartfelt." He is an "everyman," ordinary--his last name is the commonest of names, Smith--, but with an independent mind that wishes to have expression; he needs to express himself and to share this expression in order to feel human, in fact. Curious about past history and real existence and fond of Julia for her rebellious acts, Winston cannot keep himself from truly living, even if it is for but a short time. When Julia tells him after they have had an erotic encounter is the woods that she has repeated this action many times, Winston paradoxically congratulates her because of hers and others rebellious actions. He does not dislike the coarseness of her language about the Party members, although no one is to speak in this way. With Julia, Winston feels alive; his spirit sings much as the little thrush they see does.

It spread out its wings, fitted them carefully into place again, ducked it head for a moment, as though making a sort of obeisance to the sun, and then began to pour forth a torrent of song. In the afternoon hush the volume of sound was startling. Winston and Julia clung together.

But, like the song of Thomas Hardy's "darkling thrush," there is a certain fatalism to Winston Smith. So, sensing that he will come to an end regardless of what he does, Winston dares to be an individual and truly live, if but for a brief time.