Built-in playhouse

My parents have been gutting their entire basement and my mom wants to put in a built-in playhouse in the basement under the stairs. She said I could design it so I have been looking for some ideas. Here is what I have found so far...I wish I had a house to build something like this for my kids. It is adorable but does not take up a lot of space because of the way the room is set up architecturally.