a-building

From a- (“in, on”) +‎ building (“the act or process of building”).

a-building (not comparable)

Being built or under construction, as a structure or a vessel.
- 1890, William Morris, chapter XXVI, in News from Nowhere:
  This talk brought us up to the house that was a-building, not a large one, which stood at the end of a beautiful orchard surrounded by an old stone wall.
- 1922, E[ric] R[ücker] Eddison, chapter 141, in The Worm Ouroboros: A Romance, London: Jonathan Cape […], →OCLC:
  "Of these nineteen ships a-building no more than two can take the water before a month be past, and but seven more ere six months' time, push we never so mightily the work."

English