This particular building has only one face to speak of when looking at the camera view and you can see from Fig.01 that it is a simple box with just a small section of cornicing and doorway modeled in 3D.
As the main light would be in the upper left I decided that this small section of geometry would help add a much needed shadow, and the doorway was created in case an interior was included.
The texture itself provided the template for the door as I found a perfect photo in the Total Textures V19
collection and decided to use it "straight from the box", as it were. I mapped the texture onto the side of the building initially, and then cut away a doorway on the mesh to match.
You can see how the geometry has been tailored to fit the texture, as opposed to the other way around, in Fig.06. As this texture is tileable in both directions I duplicated it so that it would perfectly wraparound the edge of the building. The red line represents the edge of the texture and the green line is the corner edge of the building.
As the adjacent wall is mainly hidden it didn't matter that the texture was identical as most of it would be out of shot.
The two windows situated in the lower half exist purely as a texture with no actual geometric depth. These could also have been cut into the building but I knew these would be boarded up. As they were already darkened by a shadow I didn't feel it necessary to model them.
In Fig.07 you can see the original window image in the bottom left corner before its color correction. I have also added in some shell damage using the inherent alpha channel to select just the area of impact.
To add in a little extra detail I painted in a thin shadow (red arrow) which is absent from the original image (green arrow). You can see in the small render in the upper left how this helps to convey a little depth where there is none.
Alpha Maps instead of Volume
Camera distance and lighting conditions wield a great influence over the way we perceive a 3D scene and so it is always worth thinking about what will actually be discernable to the eye. There is little point modeling the mortar in a brick wall if it is not close enough to the camera to be noticeable. Bump and normal maps are often a more sensible and economic way of conveying such levels of detail so always bear this in mind.
A good example is the gangway between the two buildings which is composed of a flat plane (Fig.08). I initially divided it into several sections in order to face map it, but in the end used Planar mapping.
The alpha channel that accompanied the texture has been used in the Opacity slot to describe the actual walkway which is made up of thin metal strips. I opted to use more geometry where there is a greater degree of volume such as the handrails and horizontal supports (Fig.09).
You can see how this selective use of geometry vs. texture works in the final render (Fig.10).
Another section which uses exactly the same approach and texture is the platform of the lookout tower on top of the distant building (Fig.11).
In order to give it a plausible scale I simply altered the Tiling coordinates within the Material Editor. This saves any unwrapping and is a quick and effective technique for more incidental areas.