I'm tired of this "females only" bullshit in apartment ads. I understand it, but I'm tired of it. If I were posting an ad looking for a roommate, I'd prefer females too, of course. They're cleaner, and even their messes are not as gross as boys' messes. But I wouldn't specify this in the ad. I would just wait until I get responses and then choose any woman who isn't a guy. Discreet discrimination is the way to go.