Here's a file for a fire escape or external stairs drawn full size so scale to suit your needs. it's quite delicate and I recommend printing in ABS like resin. I printed the examples in 1/76 on an Elegoo Mars 2 resin printer, it just fits in the build area.
The photos are of finished models in situ on Greg Brook's Shenston Road and Kier Hardy's Hornsey Broadway model railways.
Enjoy
Jonny
Fire_Escape.stl |