From mega- + building.
megabuilding (plural megabuildings)
- A very large and imposing building.
2008 June 8, Pilar Viladas, “A Lot-Ek Solution”, in New York Times[1]:Indeed, while the big boys were designing their supersleek megabuildings, it was Tolla and Lignano’s container fetish that got them not one job but two.