Expansion is part of the core game
Tiny Eden starts with an indoor garden and expands the apartment toward the rooftop. The official description connects that growth to planting, harvesting, cooking and selling, so new space is best understood as part of the same loop rather than a separate mode.
Plan for flexibility, not a fixed meta
No official page currently gives a verified order for rooms, balconies, equipment or rooftop access. Leave enough room to respond to the conditions of the plants you are actually growing, and let the current save’s goals and interface guide purchase decisions.
What to verify before following a walkthrough
Check the game version and your own progress screen before relying on any third-party unlock advice. Costs, requirements and the order of expansion are exactly the kind of details that can change between builds.