A jack is a device for hoisting or lift heavy objects. You can use the word as a verb - "I jacked/raised up my car so I could replace the tyre". A spire is a conical or pyramidal structure that sits on top of a building and terminates to a smallish point. Imagine a flagpole that is very wide at the bottom, but ends very narrow or at a point - that is something like a spire. In your example, a secret spire was built just below the roof of the building. Then it was raised/hoisted/jacked through the roof so that the bottom of this spire sat on the roof with the peak/top of the spire going many metres higher.