What makes a bathroom a great bathroom?
First, the mundane design requirements are locating the fixtures. Even the most wonderful bathrooms have plumbing drains, water line and vent stacks, and electrical wiring in those walls. A good contractor will help with the most efficient layout, and with code requirements.
Good lighting is important, and frustrating if not done right. The most critical area for bathroom lighting is the mirror area. Wall mount lights on each side of the mirror, and another above it.
A freestanding tub can be a focal point and have a powerful impact on the decorating style. Freestanding tubs can be claw-and feet style, a pedestal base, or streamlined and straight sided.
A spa shower is a must for a dream bath. Low threshold, or no threshold bases are both practical and luxurious. Built in seating, a variety of shower heads, glass shower walls and door, with stunning tilework will make that bathroom awesome.
A few options that add detail and comfort are heated towel racks, and your favorite tile on the floor.