An easy source of O gauge ladders is N gauge sectional track. An envelope of six sections of N gauge track goes for a couple of bucks but I have found it for less than one buck at train shows and garage sales.
Use a utility knife or other pointy knife to remove the tie ends from each section side and then to remove ever other tie in the center. This will leave about on scale foot of space between each rung.
Simply glue to the side of building with Goo, Pliobond or any other contact cement.
Paint if desired.
Two examples of ladders less than one N gauge section long, glued directly on the side of the building.
Below are two examples of over one N gauge section of ladder with a more realistic off set from the building. This is useful with roof overhang. Remember to extend the ladder above the roof for safety. Ladder safety cages were not required in the 1950's, my modeling period!
Here are some more ladders on my turntable.
I have added ladders to several other industrial buildings where appropriate.
Charlie
