Definatly impossible to have one in a reef because of the amount of room needed for the ray to move around, but if you want one i would get a super wide tank that isnt too deep just wide and long. If you want to learn more or want to talk to many people who have or own rays. I suggest that you go to GrimReefers.com. They have full section devoted to rays.
I hope i helped.
I love the Grateful dead