Don't Need 'Em All

Riddle: How many 1 foot by 1 foot bricks would it take to complete a building that's 20 feet long on all four sides and 20 feet high?

Answer: Only one; the last brick you put in will complete it.

Source: https://www.riddles.com/97

How many 1 foot by 1 foot bricks would it take to complete a building that's 20 feet long on all four sides and 20 feet high? — Don't Need 'Em All by Anonymous v1.

Riddle: How many 1 foot by 1 foot bricks would it take to complete a building that's 20 feet long on all four sides and 20 feet high? Answer: Only one; the last brick you put in will complete it. — by Anonymous v2.