A sukkah cannot be more than 20 amahs high and it cannot be lower than 10 tefachim.
The opinion of R Avraham Chaim Na’eh is that an amah is 18.9 inches. According to the opinion of the Chazon Ish an amah is 22.7 inches (Frank, The Practical Talmud Dictionary) there are six tefachim to an amah.

Question: What is the tallest possible sukkah to the nearest foot?  Give the answer according to the Chason Ish and of R Avraham Chaim Na’eh .

Answer: 
According to of R Avraham Chaim Na’eh:
20 amahs x 18.9 inches = 378 inches = 31.5 feet
According to the Chazon Ish:
20 amahs x 22.7 inches = 454 inches = 38 feet

Question: What is the shortest possible sukkah in feet to the nearest foot?  Give the answer according to the Chason Ish and of R Avraham Chaim Na’eh
Answer: According to of R Avraham Chaim Na’eh:
10 tefach = 1.67 amah
1.67 amahs x 18.9 inches =   inches = feet
According to the Chazon Ish:
10 tefach = 1.67 amah
1.67 amahs x 18.9 inches =   inches = feet