It's a Yaoi manga, very short, probably a one shot. The story goes that a lonesome guy goes to the rooftop and meets another guy lazing about there. He begins to talk to him and they soon begin to engage in sexual activities on the rooftop. As time passes, the main character comes to know more and more about the boy on the rooftop, and finds out that he used to be in love with an art student in his very school.
Basically the story ends with the main character finding out that the boy on the rooftop is actually the ghost of a guy who committed suicide, and helps him to leave the mortal world by showing him that the art guy did actually love him back, by showing him the portrait he painted of the rooftop guy.