A lot of things from the H0 scale (1:87) model railroad can be used, including boxes, crates, bridges, and a thousand things more. Even buildings can be used in some cases where the doors are not too visible, since they most clearly show the scale. Check out these manufacturers: Faller, Kibri and Heljan.
I am using Linka molds to make buildings and ruins in 1:72, and it works great.
Linka You could also take a look at
Tracks and Troops, they have a lot of buildings and accessories as well.
Hope this helps!