When I was a child in the 1940s and 1950s the petrol stations that I saw were not normally custom built. They were in buildings built for other purposes and adapted, as shown in the photo. They were always known as 'garages'.
In rural areas, though, where space was not at a premium, there were garages that might be called custom-built, although they were more like elaborate sheds.
Garages did more than just sell petrol. They invariable employed mechanics who could make repairs to cars. In those days, car engines were not as complex as they are today, so it was not unreasonable for mechanics to be adequately familiar with the engine of any make of car.
For much of my life and earlier, it was unheard of to fill one's car oneself.
All garages had one or more attendant who kept a look-out for customers and came out to them to fill their cars. The driver paid through the window; change was brought back to him; and he never had to get out of the car.
Garage attendants always seemed to wear dirty overalls, so perhaps filling cars was dirtier in those days or perhaps the attendants also doubled as mechanics. Either way, customers kept their hands and clothes clean.
The design of petrol pumps changed over the years. The following pictures are presented in what I believe is approximately date order. However, almost certainly designs were phased in and out.