I recently made this set piece for a desert level I was working on. Here is my work on it at various steps!
The first thing was to draw a concept-- this took a few iterations, but by this point I was pretty happy with it.
Next I built a base model to import into Mudbox. The base model is a very simple shape that just gives us a good start to sculpt from. A good base model uses quads to avoid issues with pinching that can show up while sculpting, so I fixed up some of the more obvious triangulated areas before moving on.
Here is my first stage of sculpting, where I try to get the larger features finished before moving on to the finer details. This is where it really starts to look like the concept.
Finally, after making the game-resolution mesh and "baking" down the details, I am able to put it in the engine. Because I intended this model to be the only one in the level, I didn't have to worry about optimizing it too much, so it was pretty fast and easy to make.