Build pads are used to build turrets, healing stations, repair stations and sensor nodes. Both the Rebellion and the Empire had their own build pads to build things on but when on the battlefield when needed to protect resource pads, mining facilities and etc. Neutral build pads can help with this to   

Buildable on these pads are:

Anti-Infanty turret

Anti-Vehicle turret

Anti-Aircaft turret

Bacta healing station

Repair station

Sensor Node