Have a good look at your shower unit before tiling. Work out the best
points for pipe & cable entries to make it easy when fixing the unit to
the wall.Also, if possible leave some slack cable inside the unit case
if space allows, this will be useful if you have to fit a replacement
shower unit in the future as you can bet your bottom dollar the mains
connectors will be sited miles away from where you bring the cable
through on your old one.