This is really one of those "it depends" things for me. Sometimes if I get horny and my roommate is awake and walking around, I tend to just take off my bottoms or work underneath them. It isn't all the time, but I think it's a hassle if I know she might accidentally open the door on me. We don't have locks. When my fiance is over, she knows not to open the door because we're probably having sex past 8pm. We see each other naked a lot, but I just want privacy to get myself in the mood.
If she is asleep or not home, I undress completely. I love to be naked.