When you build your regular tech building, a new construction tab will come up. From this tab you can build two things. The Advanced Tech Center and a Crane (Crane will build twice as fast and cost half as much).
The Advanced Tech Center allows construction of super powerful structures/units and a new special ability.
GDI and Nod:
(Structure) Liquid Tiberium Spikes $2500
Scrin:
(Structure) Tiberium Glaciers $2500 (Does the same as spikes)
Nod:
(Structure - Defense) Obelisk Supreme $10,000-
A extremely large obelisk that can attack air. It has very high splash damage due to its extremely large beam of light. Anything directly hit by this beam will die. Only one of these buildings are allowed to be constructed. The power required to use this building is equivalent to 13 obelisks of light. Health = MCV's
(Unit - Infantry) Black Hand Reserves $5,000-
Basically black hands with laser chain guns. Come in squads of 10. Detect Stealth. Each guy is powerful as a venom. They can attack air.
(Unit - Vehicle) The Sathanas $8,000-
Gigantic Avatar with a beam cannon that can attack air units. Health = MCV's It's beam is twice as powerful as the obelisk of light. It has the special ability to make units next to it stealth, but it itself isn't stealth.
(Special Ability) The Word of Kane $3000 (Every 5 Minutes)-
Turns all units with in the target range to your side. Works on aircraft.
GDI:
(Structure - Defense) Advanced Guard Towers $2500
Play Renegade. Health = Sonic Emitter. Can attack air. Uses as much power as the sonic emitter. Range is Sonic Emitter x 1.5. (You can build as many as you want)
(Unit - Infantry) Mosquitoes $800
They can only fly. They have the same rifle as the zone troopers. They make the most annoying sound in the world... They attack both air and ground. They come in squads of 1. Health is the same as zone troopers. (These guys build very fast. Riflemen Fast)
(Unit - Vehicle) Hover Mammoth Tanks $3500
They Friggin Hover. Can climb over cliffs and hover over water. They also move twice as fast. They are constructed in half the amount of time it takes to build a regular Mammoth MK3.
(Special Ability) Tiberium Cleanser $3000 (Every 5 Minutes)-
Destroys all Tiberium within the target range.
Scrin:
(Structure - Defense) Storm Rider Hive $20,000
It's very large and tall. Health = MCV. Has 10 Storm Riders. Requires ten times as much power as the storm columns. Range is 3 times as large as the range of storm columns. Only one is allowed to be built.
(Unit - Infantry) Buzzer Clouds $4000
Buzzers that are 4 times as big as the normal.
(Unit - Vehicle) The Angelina Jolie $3000 (According to the Alien AI this is the closest word in the English language that can describe this unit)
Every 12 seconds a Visceroid is spawned from this unit. The Visceroids follow this unit around and attack for it. The unit is as big as a mammoth tank.
(Special Ability) Create a Tiberium Crater $10,000
GDI seems to be getting the worst deal out of this becuase they only get hovering and speed boosts, not any superpowerfle weponary.