Most people who lived in the Iroquois nation lived in longhouses. A longhouse is just what it sounds like, a long house, built of thin bendable wood, with branches woven in and out of the joists. On the outside, people used slabs of bark to make a waterproof covering. The Iroquois built their houses out of wood because the area where they lived (modern New York State and Pennsylvania) was heavily forested, but it didn't have much good building stone, or clay for bricks. So wood was the most appropriate choice for the Iroquois.
Longhouses were big enough so that a lot of people could live in one longhouse. Usually you lived with not just your mom and dad and brothers and sisters, but also with your cousins and aunts, and your grandparents. But only the relatives on your mother's side. Your relatives on your father's side would live in a different longhouse (but generally nearby).
People in Iroquoia mostly didn't build public buildings like schools or churches or courthouses then. Anything where people needed to meet usually took place outside, instead, or in somebody's longhouse. The longhouses were big enough to hold a lot of people.
Learn by doing: compare Iroquois longhouses to medieval European houses
More about the early Iroquois
Native American architecture