What is the Antonym for word edifice?

There isn't a perfect single-word antonym for "edifice," as the word carries a strong connotation of grandeur and importance. However, depending on the context, you could use words like:

General opposites:

* Shack

* Hut

* Dwelling (less grand)

* Structure (more neutral)

* Building (more generic)

Opposites emphasizing lack of permanence:

* Tumbledown

* Ruin

* Derelict

Opposites emphasizing lack of importance:

* Hovel

* Shed

* Outbuilding

The best antonym will depend on the specific context and meaning you want to convey.