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First we clean the model of polygons that we wont see in game like bottom of the model
Apply UVW unwrap modifier
Select face in modifier rollout and start selecting faces.
Select only faces that you can see. Door and window frames are unwraped later on.
When you press on quick planar map in modifier window, you flatten those faces and seperate them from other faces.
To select more faces together, hold Ctrl and select as many faces you want with left mouse button.
Every batch of faces that are flatten put on separate from others so we can organize it later.