Define the person and the task
Write who uses the room, whether assistance is present, which mobility devices enter, and how bathing and toilet transfers happen. Dimensions without a use scenario can still produce an unusable room.
Require comparable construction scope
Every proposal should state demolition, hazardous-material handling, framing/blocking, plumbing, electrical, ventilation, waterproofing system, drain work, floor transitions, fixtures, permits, inspection, cleanup, and temporary facilities.
Document what disappears behind walls
Photograph blocking, plumbing tests, drain slope, and waterproofing stages before finishes cover them. Keep product data, warranties, inspection approvals, and final control locations.
Rules, programs, and conditions change. Confirm requirements with the official source, local building department, and qualified professionals.