In Warzone2100 two groups of structures exist: defensive structures and base structures.Factories are needed to manufacture units: Factories produce tanks, Cyborg Factories produce cyborgs, and VTOL Factories produce VTOL aircraft.
Base structures are used to extract oil, produce units and research technologies while defensive structures are used to defend your base structures.
Factories and VTOL Factories can be upgraded with Factory Modules up to two times. This will add 100% to its production rate multiplier and allow production of larger tanks/VTOLs. One Factory Module is needed to produce tanks with medium bodies, and two Factory Modules on the same Factory are needed to produce tanks with heavy bodies.
It takes a number of seconds equal to weight/100 to rearm a VTOL, before rearming pad upgrades.