Example 4: An owner has Apartments each with 2 bedrooms, they can be sold as 1 and 2 bedroom apartments.
(Apartment A1 - 2 bedroom and A2 (1 bedroom) - Apartment B1 (2 bedroom) and B2 (1 bedroom). Apartment B2 is only available when Apartment A1 and A2 are unavailable)
1. Set up your rooms: