What is preferred lacing for PowerTap wheel build?
According to the FAQ on their website:


  Note: PowerTap hubs must be laced with a minimum 2 cross pattern to avoid damage to the hub and maintain the warranty."


That suggests that making the non-drive side radial could lead to warranty issues. Radial lacing does stress the flange more than tangential lacing so many hub manufacturers do not allow it. To work on a driven wheel it also needs a certain amount of torsional flexibility in the hub which large-flange solid hubs don't have (Rohloff, PowerTap for example).

I would go with a ye olde traditional 3x lacing, and lean more towards 2x and bladed spokes than other options if the rider wants to spend more money.