Preparing Building in Blender
Need to know
- How to work in Blender
 - How to work with Blender X-Ray Addon
 - What is a Static Object
 - What is a Portal and Sector
 
About
Buildings should be created according to a special pipeline. This is necessary for future creation of Sectors and Portals for optimization.
Start

The idea is to separate the inside and outside of the building.

note
Orange indicates the outer side.
Blue indicates the inner side.
Finish
Go to Object Properties.
In X-Ray Engine: Object select Static in the Type list.