Direct answer

Reach the rooftop by completing the room โ†’ atrium โ†’ lab expansion chain, then build the greenhouse. Unlocking it aligns with the Hothouse achievement.

Path

  • Complete earlier room/club expansions.
  • Finish the lab construction chain.
  • Build the rooftop greenhouse when available.
โœ“
Evidence note

The rooftop is the confirmed final expansion; exact build requirements are in the progression dataset.

OBSERVED

Greenhouse electricity billing before unlock is a reported quirk โ€” logged in troubleshooting.

Troubleshooting
โ„น

Hothouse deep guide expands on the achievement trigger.