The Tech 1 Construction Bot is the cheapest construction unit in the game. It is slow and weak, so it may be prudent not to let it wander unescorted. It surpasses the Commander as a constructor with its ability to build advanced T1 structures, including the T2 Bot Lab.
Use in groups for increased build power.
To build even more advanced T2 structures, you first need to build the T2 Construction bot in the T2 Bot Lab.