What do you define as "built"?
Someone could be here all day explaining the step by step process.

For one, it depends on the carrier. Not necessarily GSM vs. CDMA but EVERY carrier carries their own design and steps to setup. For example, even though Verizon and Sprint are CDMA (based) they DO NOT make identical towers with identical technology. GSM and CDMA carriers have VERY different towers and technology.

Also, some towers on one carrier may vary from tower to tower. For example, some carriers use a "base tower" this means that many carriers use the same tower. NO this is NOT roaming. This is where there's basically a long pole in the air. Each carrier comes and attaches their own technology on to one tower. This just speeds up the government approval part. These towers look like they have multiple triangles on them.

both the tall ones and the smaller pipe looking one.