Extractors are your most efficient source of income, and probably your main one aswell. They can only be placed on empty resource pools spread across the map, which limits the maximum Extractors per level, and makes it harder to protect and maintain them.

The Extractor is most likely the first structure you'll build, as the first one provides for a massive boost in economy, from $12 per tick to a whopping $20 (67% increase!), and a strong economy is the key to succes in any RTS. In any default match you'll start with 1 builder and $4000 cash, so it is possible to build other structures before your first or second Extractor, but it is not recommended.


T1 Extractors:

• 800 HP
  
• $8/tick income

T2 Extractors:

• 1000 HP
  
• $12/tick income

T3 Extractors:

• 2000 HP
  
• $18/tick income

Building an Extractor costs $700, making it one of the cheapest buildings available.

Upgrading from T1 -> T2
Price: $1200
Effect: +50% credit generation (+$4), +200HP

Upgrading from T2 -> T3
Price: $2500
Effect: +50% credit generation (+$6), +1000HP


There are two sides to consider before making this decision: the economic and strategic side. Economically, in any case, building a new Extractor is more profitable than upgrading an old one, as it is cheaper ($700 in comparison to $1200 or $2500) and has a higher income increase (+$8, instead of +$4 or +$6).

However, strategically thinking, you would have to build defenses or waste units on defending the new Extractors, in order to prevent a quick takedown from the enemy player/AI. Adding the price and building time of the defenses, and/or the price and building time of the units defending the structure, plus the fact that these resources could have been used anywhere else on the battlefield, make building another Extractor a rather tough decision.

It's mostly situational. If there are empty resource pools near your base, or behind your base, it is obviously safe to take them. The further you build them towards the enemy base, the more careful you should be, and the higher the defense costs will be.