The rationale for building is simple. We couldn't find a house on the market that met our needs. Strange as it seems, nothing we looked at provided a master bedroom and additional bedroom on the main floor, and a separate living space for the third adult in our family. Basically, we wanted a 2 bedroom up and 2 down rambler with a daylight basement.
Of course we had other things we wanted, some pretty much requirements, some nice to have. Of the former, designing for seniors was a requirement. Architects and builders call this being "ADA Compliant," which refers to the Americans with Disabilities Act, I guess that means we older Americans are considered disabled. Sometimes I feel that's accurate, especially in the morning before I've had my coffee.