Best method for creating a bath cut out in a raised level

[Mr Oz]

Hi I have a client who would like a step up to a higher level in a bathroom where the bath will then be recessed into that level so its flush with the higher level floor surface.

Can anyone suggest the best method for achieving this cut out function. I tried using a custom counter top but couldnt see how you could create a hole for the interior of the bath.

Regards