Which schedule suits your building?
Fixed schedule: every household has the same slot every week. Simple and the most common – works well if the times suit everyone.
Rotating schedule: slots move on every week, so nobody is stuck with the unpopular Saturday evening forever. Good for buildings with many households and few slots.
Sign-up sheet: a monthly sheet with empty boxes. Whoever wants to wash signs up. Flexible, but only fair if everyone sticks to it – and nobody books the whole month in advance.
Note: your building's house rules (Hausordnung) and tenancy agreement take precedence. Best discuss a new schedule with the property management (Verwaltung) or caretaker (Hauswart) and agree on it together in the building.