The cost of granny flat construction can feel like a mystery, but you can crack it with the right data and a clear plan. In this guide I’ll walk you through the big‑ticket items, state‑by‑state permitting quirks, per‑square‑metre pricing for different finishes, and the hidden expenses that bite most owners. You’ll also get a realistic timeline, financing options, and a quick case study from a Melbourne backyard cottage. By the end you’ll know exactly where to focus your budge