Primarily a plumber or wet-room specialist will need to ensure a gradient is levelled to make water drain away easily. It is also recommended that you install underfloor heating, not only to provide warmth underfoot but to help water evaporate from the tiles quicker.
The floor will then be coated with a membrane. Some people choose this or an effective mat system which in reality is just one big rubbery like shower tray. The important distinction to make is you could effectively have the shower head anywhere and design wise make it a centrepiece of the room. While some people choose to lose the bath altogether and end up with a glorious shower room, others wish to keep the relaxing tub within.
Also why have one shower head when you can have three? And have you considered a pressure shower that shoots water at you from different angles? These are often termed massage showers. The units like cabinet, toilet, bath, mirrors and lighting would need to be fully waterproof.