The longhouse is the Iroquois unique building. It replaces the workshop and instead of speeding up building production by 10% like the workshop, it gives the city +1 production from each worked forest tile.
Historical Info:
For much of their history, many of the Iroquois people lived in villages containing one or more "Longhouses", communal buildings constructed of wood saplings sheathed in elm bark. In fact, the Iroquois call themselves "Hodenosaunee", which translates into "People of the Longhouse". The longhouses ranged from 40 to 400 feet in length and some 25 feet wide. They were divided into compartments by inner partitions, each connected by an open center aisle. Several compartments would share a cooking fire in the center aisle, with an opening in the roof above acting as a chimney.
Longhouses are efficient structures, cheaper to construct and heat than individiual dwellings, thus requiring fewer natural reseources than other types of home. They are representative of the Iroquois' cultural desire to survive and thrive in harmony with the environment around them.