Dual shower head

Quick question: I'm remodeling the bathroom. I will be doing the plumbing myself. My wife would really like two shower heads (one on either side of the tub). I will be running a 1/2" copper mix line to the first shower head. Can I just tee off and run another 1/2" to the other shower head, or should I drop down to 3/8"? I am planning on putting a manual valve on the 2nd shower head to turn it off when not wanted.

Thanks in advance.

You could purchase a nice diverter valve that will let you switch from head a or b or both. and run 1/2" to both.