Glenn took a liking to Maggie, and she seemed to have a right head on her shoulders, that was enough to win Daryl's favor. He viewed her as a part of the group and he knew Rick would have done the same. Even if he didn't plan on becoming her best friend, he wanted her to know that he was here and find out what she knew.
As a matter of fact, Daryl didn't like the net. He'd never texted or used a phone much before the apocalypse and he didn't want to now. He just wanted to talk to people face to face, was that so much to ask?
Carol walked out onto the roof and Daryl took it as his cue to stand up. He pulled himself up, leaving his crossbow on the ground. He nodded back in reply, glancing down at the gun holstered...that was good. She ought to keep it on her. Before he had a chance to say anything about Maggie showing up, she was walking out onto the roof with them, looking more excited than he'd bargained for.
Instead of greeting her back like he should have, he felt a wave of trepidation and asked in a level tone "You come alone?" He knew Glenn wouldn't have left her side since he was all starry-eyed about her. If something happened to that kid, Daryl really would mourn him. He just wanted to know before they got into anything else. Social graces had never been his strong point, either, let Carol take care of the niceties.