Definitely second Lon's observation ,on Keith's tweaking of the domes on the pumps. As they look nicer than my own.
As for buildings its more a case of deciding on the storytelling aspect of your Garage/ Petrol station as this effect both the type of building you use and the location of the pumps themselves
If your after representing an early and or Rural station.Then these look absolutely nothing like a petrol station. As mentioned they look more like a house. The easiest building to use for this is a building with an arch under a portion of the building which is fenced off and enclosed with a wooden wall/gate . Rather than just a 'house'
The Pumps were often placed against the front of the building and at the edge of a road. There are no forecourts or parking bays . It's literally building on a curb with the pumps squeezed in-between the two.( This is the most common format from the twenties onwards. In fact you can still roll through a few villages today and come across this format ( not in use but still institute.) especially in areas where it's down to single lane roads.
The next evolution is the moving of the 'diesel' pump to the rear or futher away from the 'home' part of the site due to the fumes of both the fuel and the vehicles that used it.
At the same time you see the proliferation of buildings for maintenance of vehicles ( the garage proper) as in the picture already posted in the thread. The main pumps are either slightly set back from the road and near the new garage building or still near the house. As it's an evolution rather than an instant build.
The forecourt proper turns up in the mid thirties as cars become more and more popular and allows for multiple cars to be fueled at the same time.
So you can look at framing your design as a 'new' build ,or something that's evolved over two generations.
But... Thats nerdy and it's how I approach a build.

The best way to represent a garage is to represent the aesthetic you visualise when it's mentioned to you as a 30's garage.
The simplest way to represent a garage is to use what ever buildings you already own and put your petrol pumps on their own separate base and place them Infront of any building you have. When you want to represent a garage.