Build a 5x5 frame of iron blocks
Stack it up 4 blocks
Destroy 1st and 2nd layers of 23
Replace with iron door
Put buttons on top
Add roof of iron bars.
Destroy 1st and 2nd layer of 11 and 15
Replace with iron doors
Put buttons on top in the inside
Follow instructions for Building except for doors and buttons.
6 11 16 = 2-3 layer iron bars.