In the '60s it was new that the average man could buy a car. This was closely connected with the increasing prosperity. The number of cars in the Netherlands grew tremendously over the decade. Most cars were (and still are) just parked on the street. A few lucky ones were able to rent a garage, usually not too far away from their home.
Traffic engineers and City planners could barely keep up with the rapid, major changes that the car brought with it. This led to many "solutions", including parking solutions, which almost no longer applied in the following decades. The groups garages are a good example.
The garages were single wall built in stretcher bond. A concrete floor and a simple flat roof finished it. Indeed, the focus was on quick and easy to build.
Some had revolving doors, other doors tilt. Originally there was usually no electricity. In many cases this is provided later.