Buildings: They create the towns, villages and workplaces on your railroad.
For a Large Scale railroad to seem real, it must have a reason for being. Railroads weren't built just to carry the trains. They were built to carry people and things to other places. So before you lay your track you might want to think about what you want your railroad to do. If your railroad is going to be a narrow gauge line set in the old West, you might think about carrying people between widely space villages or towns. You might want it to haul some freight as well. Perhaps, the railroad will carry cattle between a remote loading station to a city where they will be turned into steaks. Perhaps your railroad will carry ore from a mine to a processing facility and also carry the miners from their homes in town to the mine. Or, if your railroad is set in modern times and is a standard gauge road, you might want to have it move containers or heavy bulk products such as coal from mines to power plants or ore docks.
Whatever the function of your road, you will need buildings to give it a reason to exist. The good news is that there are many buildings out there for you to purchase and place directly on your railroad. You can also find building kits or build the buildings to your own specifications using materials available to make that job easy.
Modeling a specific timeframe requires you to pay attention to the overall design of the building, the size and shape of the doors and windows and the technology used in the time you are modeling.
The area of the county you are modeling should determine your choices in selecting the type of building you want to have on your railroad. The West and Midwest have a distinctively differently styled homes and shops than those in the East or South.
You will need houses for all areas of your railroad. Stores and shops will be required for your villages, towns and cities. Factories, refineries and other buildings can be used as source of freight for you railroad. You will also want several buildings for servicing your locomotives, cars and other railroad equipment.
As you can see, the possibilities for buildings probably exceed the space and money you have for them. Therefore, it is important that you decide what you want to include early in the planning process. Most of us don't have the space for a complete town or even a complete village, so we need to find a small number of buildings that suggest what we want to create.
If you railroad is outdoors, you will need to be concerned about the material used in the buildings. Many Large Scale buildings are made of heavy plastic that are weather-resistant and resist ultraviolet radiation that comes from long exposure to the sun's rays. Some are built from cedar or redwood which weather, but remain serviceable for many years.
Indoor railroads don't require the same kind of durable buildings as outdoor ones. Indoor buildings can be constructed of vinyl, basswood, balsa or even cardboard or paper.
Just remember that planning for your structures in the beginning will make your railroad seem more real. You need to have the structures provide the reason for your railroad to exist.