Even though we weren't supposed to be up there, my favorite part of my house was the roof...off our room, there was this one large flat part and we'd go out there and study or hang out. Our house was in the ghetto, basically, so it wouldn't be the safest thing to be outside at night sitting around. With the roof, we could all be outside when it was 100 degrees inside and not have to worry about anything. I'd highly recommend a large balcony, if it's doable.
We also had this HUGE basement which we couldn't use because of fire codes. We all thought it would be nice to have a big room downstairs where we could have the TV and couches and so on to hang out in so we wouldn't have to use the chapter room for that. It would've kept the chapter room much nicer and would've had room for more people to sit comfortably. Instead, it just got piled with boxes and random crap.