Modelling

Since the source for references is Borderlands, I am able to use the game itself to collect reference material or move around the model itself. As such it was an easy process to go straight into the modelling stage.

Here is the low poly version of the Zed building made by extruding a single cube and inserting edge loops.

 At this point I smooth it then change it to the Smooth Mesh to Poly convert...

Finally, adding in the extras like vents, water towers and columns, Zeds building is finished. The long part of Zeds can be cut in half and duplicated to make Marcus' building.

This is the New-U station (Spawnpoint in Borderlands). The wire was made by extruding a cylinder along a curve.

Lastly, these are some assets that will be duplicated around the level as clutter helping to fill the scene.