Cottage is the fifth unlocked residential building in the game. It is available after having researched the Cottage technology in Iron Age. It provides as high as 73 population which is higher than any previous residential buildings but only a gold production rate of 110 Gold over 4 hours which is relatively low. Making it less efficient.
However, when players come to late Iron Age, many technologies require goods to unlock, which means players need to build Goods Buildings. Largely Increased the demand of population and here Cottage come in handy.
It is recommended to build a portion of residential buildings as Cottage, players have to take balance between population and gold production.