That looks amazing! I have a question though, as I am in the middle of building something similar for our boys.... Are you not concerned about them gnawing the wood?
Our Albert is a real chewer and has now had a go at every single chair leg in the house - no matter how many gnaw logs/treats/parsley bells/willow tubes/seagrass mats [etc, etc] he has! I proudly put my semi-complete creation on the floor the other day, turned my back, and turned round to find he had already scurried over and taken a big chunk out of one side! I swear he ran off laughing!
The wood he attacked was a generic 'softwood' from B&Q, so maybe plywood is less tasty? I'm concerned about them eating it though if it is actually Pine as I understand this can be toxic. I'm also concerned that they would chew threw the paint [it was painted when he attacked it so the smell/taste obviously didnt put him off].
How do you think your girls will treat the wood? Are there any tricks you'll be employing to stop gnawing? Any ideas would be great - at the moment my solution is to cover the inside frame with a perspex window that they cant get any traction on to gnaw! - an expensive solution though!