Most of the comments above were made when the game was in early Alpha development and before the creation of multiple floors, which greatly changed floor sizes 
In Alpha, we had to build large houses, often 10x15 to 14x21 being common, to meet the 5 large rooms requirement for advancement for the earliest Foundies.
Now with multiple floors (11 max) we can build on much smaller footprints. A 5x5 to 7x7 house is easily large enough at 25 to 49 squares compared to at least 150 squares for an Alpha built house.
A note on room sizes:
11 squares total is the minimum for a big room i.e. a 4 x 3 tile room.
Also note that there was a 11 Foundy population maximum in early Alpha games compared to 13 now.