From Halopedia, the Halo wiki
Base types: Minibase • Firebase • Combat Station • Command Center • Headquarters Stronghold (Only in Stronghold)
Base slots:
Airpad • Armory • Barracks • Garage • Generator (Advanced Generator) • Supply Pad (Heavy Supply Pad)
Turret sites:
Base types: Minibase • Outpost • Stronghold • Citadel • Fortress Stronghold (Only in Stronghold)
Apex • Foundry • Harvester (Augmented Harvester) • Power Extractor (Augmented Extractor) • Raid Camp • War Council
This is a template that lists buildable structures in Halo Wars 2.