3 Gate Robo
From Liquipedia Starcraft 2 Wiki
The 3-Gate Robo is a standard Protoss build order useful in all matchups. It is meant to handle early pressure in close positions without sacrificing tech or the ability to expand once the opponent does. This build deals especially well with massed-unit strategies, and it sees frequent use in PvP matchups as the standard route to the Colossus.
The purpose of this build is to be able to tech safely to first a second mining base and then Colossus, off of three Gateway and Observer for spotting. Immortal support is dependent on the opposing player using units with armor-attribute like Siege Tank, Roach, Stalker-heavy armies; otherwise mass Zealot and Stalker/Sentry is used to hold off aggression.
 Basic Build Order
See SC2planner build order (3 Gate Robo)
- Start saving Nexus energy for Chrono Boosts when you start the Stalker for use on Warpgate Research for massing Gateway units as needed.
- Produce mainly Zealots from your Gateways while your Robotics Facility is building. After the Robotics Facility completes, make an Observer and throw down your Robotics Bay as soon as you have 200 minerals and 200 gas which should occur at about 45 supply.
- Delaying Colossus tech in favor of necessary Gateway units is possible, although one should not rely solely on Gateway units for too long.
- Never allow Colossi to engage enemy units without Gateway support. The long build time and high cost of a Colossus mandates that one attempt to preserve as many of them as possible throughout the game.
- When scouting the opponent's base, look to see if the opponent is mining gas. If they have not built an Assimilator, Extractor, or Refinery, it is likely that they are looking to rush with early units. If this is the case, one may want to cut probes or delay construction of the Robotics Facility until these threats are met and dealt with.
- The scouting Probe should be sent at 9/10 after building the Pylon, as it maximizes the possibility that it will get into a Terran base before they wall off.
- If the opponent counters the Colossus with dedicated anti-air units (Phoenix/Viking/Corruptor), temporarily switching to Immortal or Archon is advised for a high health, front line unit. If the opposing air units are Mutalisk or Banshee, building own Phoenix are highly effective against these units, producing a few will give air control and the possibility of continuing Colossus production.
This build is susceptible to air units, which is why an early observer is necessary in order to scout for a Spire, Stargate, or cloaked Banshee tech. If one opts not to expand, this build cannot support both Colossi tech along with anti-air units. On one base, saturated gas mining (3 in each geyser, 6 total) will only produce around 225 gas per 60 seconds of game time. At most, one will be able to produce roughly 1 Stalker each minute in order to be able to produce 1 Colossus continuously (Colossus build time is 75 game seconds without chronoboost).
- Thermal Lance Upgrade: Since it costs the same amount of gas as a Colossus, researching this upgrade too soon effectively limits one to 1 less Colossus for a certain amount of time. It depends upon whether or not the upgrade or the unit will bring the greater benefit. In PvP against an opponent who is also producing Colossi, it would be unwise to give them the numbers advantage while you have to wait for the tech advantage. At some point you will need to expand if you want to keep producing colossi and get the upgrade. You need the extra gas income if you want to be able to make colossi easily.
When one takes a second expansion (third base), it is advised to build a second Robotics Facility to build more Colossi/Immortals. This is highly recommended in situations where it is evident that the enemy is not adapting well to this strategy. Alternatively, one might choose to add another layer of tech to bolster the already successful main force.
A common response to Colossi is to produce dedicated anti-air units (Phoenix, Viking, Corruptor) to directly attack one's Colossi. Continuing to produce Colossi for the long term is not advised, as losing these units is costly and also robs one's forces of valuable damage against massed units. At such a point one should already have a Twilight Council for the purpose of getting Charge or Blink, so the next logical progression is to build a Templar Archives and produce High Templar. Short term Colossi may be necessary to buy time for Storm to complete, but make sure that further gas goes to Templar production. This both erases the effectiveness of the anti-air units while maintaining a strong army capable of area damage via Storm.
Should the dedicated anti-air not come, another transition along the same lines is to build a Dark Shrine and add Dark Templar to one's main army in small numbers. These units will do further damage while undetected by one's opponent. They are faster than High Templar and can move with the army, and will add to one's damage output greatly. They are also excellent for map control in the mid-late game.
Massed air-to-ground units (Void Rays/Mutalisks/Banshees) require switching out of this tech in favor of Blink Stalkers and more Gateways. Immortals/Observers can be produced if the Robotics Facility is idle.
Facing Siege Tanks requires Immortals instead of Colossi.
 Pro features
- Narrow choke points where the Colossus' Thermal Lances will damage clustered units.
- Multiple elevation changes where Colossi can take the high ground and attack without the possibility of return fire.
 Con features
- Wide open spaces where high DPS units can spread out and surround the Colossus.
- Maps with large air spaces surrounding bases that call for air abuse/harassment.
- HuK (P) vs. Adelscott (P) - NVIDIA GosuCup Grand Finals
- SjoW (T) vs FremAN (P) - SHOUTcraft tournament, TotalBiscuit commentary
 External Notes