WHAT IS IT?

I came home from work a few evenings ago to find this larger-than-I-expected structure in our backyard.
  1. A playhouse for our girls?
    As I was led to believe?
  2. Brother husband residence?
  3. Craft Corner?
  4. My old biddy shack?
  5. Seriously, it's way bigger than I thought it was going to be.