Creating modules for environement use?

Thanks for the info. When i create the Box brushes into static meshes, it completely removes all of my doorways. Is there a reason for this?

Ideally, i am trying to create an architecturally correct unit to make as a modular element so we are then able to import it into other levels.

Do you have any ideas or alternatives as to how this could work? As the original process, i learned to create these units was by using box brushes as walls and subtractive box brushes to create door ways.