Allies[edit]
The Allies use the build system traditional to Command and Conquer. When a building is selected to be built at the ConYard, it is built up over time and then when deployed, it is instantly ready to use. The buildings do not give ground control however, so you will need to expand your base by relocating your MCV or deploying Prospectors into Command Hubs.
To use higher tier units, deploy your MCV or Prospector near your Boot Camps, Seaports, Armor Facilities and Airbases and upgrade the MCV or Command Hub to Heightened (tier 2) or Maximum (tier 3) clearance. In other words, the Tech level of the Allies production relies on the very locale of such "Tech center".
The Allies have bigger ground control (than the Soviets) when it comes to deploying their MCVs and Prospectors.
Soviets[edit]
The Soviets literally build up their structures on the map, with construction sites set up. While being built they are unusable yet vulnerable. When finished they can expand ground control. The Soviets can also build a Crusher Crane to unlock a second build queue.
To build tier 2 units and structures, build a Super Reactor; to build tier 3 units and structures (e.g. Vacuum Imploder), build a Battle Lab. In other words, the Tech system of the Soviets bears Red Alert 2 (probably all C&C?) tradition, that the Tech level of all productions relies solely on whether the player has the key buildings or not, regardless of location across the map. This also leaves a possibility (although quite rare) unique to the Soviets that, if the player somehow has Battle lab (and production buildings) but no Super Reactors, then s/he will be able to produce tier 1 and tier 3 units, but not tier 2.
Like the Allies, the Soviets may use some special unit (Sputnik) to deploy and expand ground control, but Sputnik (Outpost) provides smaller Ground control than Prospector (Command Hub).
Empire[edit]
The Empire's build system is very unique. Structures come out of ConYard in the form of little Nanocores, which can traverse both land and water. They can unpack into structures anywhere on the map. This system is good for grabbing Ore Nodes quickly. The Nanocores are vulnerable to attack however, so escort them with Tsunami Tanks and Mecha Tengus.
The major drawbacks to Nanocores are that they build up structures slow and they provide small ground control (for Walls).
Among the Tech systems of the three countries, that of the Empire is arguably most expensive and time-consuming, because to access tier 2/3 units, each production building (be it Dojo, Mecha Bay or Dock) has to upgrade separately, spending much more time (counting for all buildings) than the Allies. This means the Empire has to be careful not to lose those top-tier'd buildings (especially the Dock); player may choose to deploy the more "expendable" production buildings (which produces more expendable units) at battlefront and keep the top-tier'd ones back in home at safe locations.