Where shared bathrooms actually fail
In order: silicone at the tray junction, extractor fans that were never adequate, waste traps blocked with hair, and taps or valves worn out by constant use. Almost none of these are tile or suite problems, yet those are where refurbishment budgets usually go.
Specify for maintenance access
Every serviceable component should be reachable without breaking tiles. That means accessible service valves on each supply, removable bath panels or access hatches, exposed traps where possible, and shower valves whose cartridges can be replaced from the front. This single principle saves more money over a decade than any material choice.
Ventilation sized properly
Continuous-running or humidistat extraction, ducted the shortest practical route to outside, is essential where showers run one after another. Under-sized fans with long flexible ducting are the usual reason a two-year-old shared bathroom is already black at the ceiling line.
Adding an extra shower room
Where a house is short of bathroom capacity, converting a box room or under-stairs space into a second shower room or WC often does more for tenant retention than upgrading the existing one. Feasibility depends on soil-pipe access and floor depth, which is a survey question rather than a plan-drawing one.