You may be concerned about an apartment because of neighbors and potentially the noise in labor, the people who attend you parking in the area and other issues of that nature. Though these are typically truly not a problem for most people. Some women have suggested talking to their neighbors ahead of time. Explain that you are planning a home birth and that they may see more people, have parking issues or hear noises, but that everything is fine. Another mother talked about a sign that she hung up at the mailboxes about a "birthing party." This alerted the neighbors once she was actually in labor.
Space is rarely an issue for the attendants. Though due to space restrictions you may have a more difficult time with a water birth. Or you may decide to limit the number of people that you invite over.
If you are concerned about the suitability of your apartment for a home birth, ask your midwife or doctor for their advice.