Decisions: These are the "Givens & Druthers".
Do you want to freelance the railroad or copy a prototype? What kinds of equipment (locomotives and cars) do you want to run? You may want to add your own rules like what you want the height of the layout to be, how wide the aisles should be if you have aisles, and you may want to make sure that all areas of the railroad have easy access, so you're not having to break your back bending over or stand on a ladder or scaffolding to reach the farther sections of your track and scenery. If you are creating this railroad by yourself, you may want to start with a small layout and add to it later gradually.
I will probably be freelancing it cause that's what I do.
What kind of cars? I like steam engines so that is what I want for my personal railroad. But what category? I like the idea of a passenger train with a sleeping car, a dining car and a baggage car.
Like the steam idea, this gives me a choice with the backdrop. I can have several unique villages or different terrains. I will probably go with the Canadian National or Canadian Pacific Railroad type.