This isn't how most modular game assets are designed. Instead, choose a pixel density to work towards, and use that as a rough guide when creating each individual asset. For example 4 pixels per centimeter, or whatever you decide.
I am using 3ds Max and the plugin PolyTools3D Advanced UV Normalizer. I am working with large buildings and also smaller objects. For the large buildings and other modular elements for the buildings I was planning on using (per the UV normalizer) a Geometry area of 4096.0m and a UV Area of 256. The pixel area is…