HO & O - High Quality Scale Modeling Architecture and Railroading

There is usually a lot of stuff on the flat roofs of commercial buildings. I've added three vents with some accumulated rust and grime. Most models get viewed from the top so my opinion is that roof tops

should get as much attention as other parts of a structure.

I'm using round vents with cone tops that would have been made of metal. I'm using pastel chalk to put down "rust" on the roof where the vents will be.

Then the vents are glued over the top of the rust marks.