For proper installation of fixtures and tile. The vanity and top must be placed in a straight setting or gaps between surfaces will appear and need to be addressed. All custom design costs more than modular pre-built showers and tiling. Bathroom renovations with custom requirements involve far more labor than store bought fixtures and increase the cost. Installing the larger rain head shower head and or body sprays require increasing the size or diameter of the existing plumbing feed due to the increased volume of the water. Changing the existing water lines requires opening up the existing wall, ceiling, or floors depending on the location of the lines. Plumbing costs have to be considered. Before decisions are made. There are quite a lot of renovations that are prerequisite before the intended renovation can begin.