Please remember that its not english so you have to think Korean in every situation.
on this same note. In korean 너무 has multiple meanings depending on the situation. this use is perfectly natural. Remember though it is Korean not English. they don't translate perfectly or exactly the same way every time.
Depending on the situation, it can also be used as "so". It is the same in English as well
Just note that "너무" has negative meaning.So the situation might be that a guy had to clean the garage and just saw the size of garage. These days korean may use "너무" without negative meaning in some cases.But this sentence sounds weird to me if he was just surprised.