Textures have become very easy to find on the internet these days. What do I mean by textures, google "wood plank textures"or go to https://www.sketchuptextureclub.com/ Now most are free which is good. You can take the picture and scale it to your needs. Make sure when you are scaling that you keep the aspect ratio on so it does not become distorted. If you are making signs you know how big you want it so you can put in the numbers for either width or height. I have pictures of stone and brick walls, floor boards, room interiors, and even a wall with boards and studs. I have also used some for signs or designed the signs on my own and printed them . When I want to make signs I print them on 20lb paper and cut them out and highlight the edge with a pencil or marker to cover the white. I then glue them with a kids glue stick to a building wall or to .05 styrene for signs that are mounted on posts. I printed the building interiors on 60lb paper. Not all will work as some will not repeat well when you join them together.What I mean by this is if you have a sheet of plywood with a big knot in the middle it will repeat the knot which is ok unless you are doing a wall. Here are some examples of textures that I have used and played around with.
It would be next to impossible to weather ceder singles to look like this in Ho scale
Here is a brick wall. Now you would maybe want to crop out the stain at the bottom or flip the picture if you are going to start joining them together.
Here is some tread plate that would be easy to scale and join together
Here are the old green 3 tab shingles that were on most houses in 1959. This one would have to be cropped to work right when you join the side edges.
Here is a sheet of OSB that will work well for a wall because it has no knots. If you scale it and glue it to say .005 sheet you can have a single sheet of plywood that you can put in the back of a half ton truck.
Here is a nice stone wall that I will be using on the exterior of the next farm house I build.
Now walls with studs are hard to find and I intend to use this for inside of my wooden grainery.
I used these wood planks for the floor in my E Class Station. You can also change the colour, darkness and the tint if you would like to.
Here are some of the signs and other details that I have used. The RBC, Barbershop, Co-op signs, the thermometer on the barbershop wall, the interior on each building, the curtains in the windows, the licence plate on the truck.
Here are interiors that I have used. You have to find very specific pictures for this to work. Then play around with the scale, print, test and try again. The interior in the Bakery is curved so you get the perspective that you are looking way back into the store. The awnings are ones that I also created and then printed.
This is the interior of an F unit and it is scaled down to fit on the wall in my camera car. I now have an interiors for a GP9 long hood forward, SD9, FA1 and an SD40. I have to make a change to my car so each slide can be changed more easily.
I also use this process for all my station, flanger, whistle, mileage, flags, yard limit and road signs. The big advantage being that you have very unique details that are not for sale to just anyone.
Any graphic art program will work to scale the textures and pictures you may have. There are a few programs that you can use. I use Inkscape or Gimp which are free and at times have used just a word doc to scale a picture to the size I want. Corel also makes a program but you have to pay for it. These programs are easy to find with a quick search on the internet. For this purpose they are not that hard to learn.