Harvester
Supply Platform
Barracks
(Clearing out Expansion & Flux Crystals with your Hero/Sol Invictus while they're building)
(Research Lab - For matches with a further away Expansion)
Expansion
Harvester
Harvester (train a third only when you have a free Flux Crystal, of course)
Supply Platform 2x
War Foundry / Research Lab (Depending on if you want Striders and/or Titans or not)
Rest depends on the Army Composition