This may be my best photo:
I particularly like the way the foreground scenery blends in with the backdrop.
If my memory serves me correctly, the backdrop was painted first, on Masonite that I attached to the walls of my basement playroom. Then, the plywood board, track, foreground scenery and trees and structures came next.
Most of this was done about 25 years ago. The thought occurs to me, and I could be wrong, that little was planned, that the backdrop was painted with latex and acrylic paints (I hate turpentine) over and over again until I was satisfied with the results (I was a poor to mediocre student in elementary school art class), and the blending of the backdrop and scenery was largely an accident.
The trees are homemade using Woodland Scenics scenery materials and real branches from my yard and nearby State park. Finding symetrical branches and making the trees was a lot of fun, and my young children (now 30 something) may have helped me make them. My objective assessment of my homemade trees is they are pretty good, not great, yet satisfactory to me.
I share these thoughts, especially for those who have their doubts about their ability to make nice scenery including backdrop. Believe me, if I can do it, you can do it.
However, if you want to have great scenery, that is different IMO; I believe making great layout scenery takes a lot of knowledge, artistic talent and skill, which I definitely lack.
Arnold