Can you make us a cat run?

This project started with one simple question,
“Can you make us a cat run?”

“How hard can that be?” I said to myself. 

Then came the details: 

1. Tunnel to get the cats from the existing door to the cat run
2. Outdoor seating to be incorporated
3. Garden tool storage
4. Other storage cupboards  
5. Large enough to walk into 
6. Include play things for the cats
7. A dark cubby hole for cats to hide in, but it must include a door to get them out if needed
8. A dividing wall to separate the cats if they are fighting 

and....