So... let me see. Obviously they know each other from Hogwarts as Roger was Ravenclaw's captain; he secretly thinks Zach wasn't as good of a captain as Cedric was, but they were also pretty good friends before he died, so, yeah... Roger was a chaser for the Arrows until he selfishly jumped ship to preserve his career; he also didn't respect the captain there and was pretty open about it.
Roger loves to party and can get a little wild. He, despite being straight, would have flirted with Zach just 'cause he flirts with anyone, he might have even teased him good-naturedly if Zach fell for it for the hundredth time.
My IM is fleeingreality. Feel free to IM me and we can hash more out!