A base is nothing without purpose.
X-Com is given a choice of simple facilities to customise any base. Any base may be designed to have a specific purpose or be built in a one-size-fits-all style.
All Government buildings available for purchase by X-Com come with a single Access Lift and a collection of blank corridors which cannot be changed but allow facilities to be built anywhere.
Every facility, basic or advanced, will take a differing number days to build and will need to be maintained.
Any base sections damaged by hostiles with explosives, when on a Base Defense mission will be automatically repaired, with cost, at succesful completion.