The most common and most likely answer to this crossword clue is the 7 letter word STOREYS
I've seen this crossword clue in The Guardian
S
T
O
R
E
Y
S
More clues leading to the result STOREYS
Buddy explains!

The straight part
We know that "different levels" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case different levels = storeys.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does STOREYS mean?
STOREYS noun- A building; an edifice.
- A floor or level of a building or ship.
- A vertical level in certain letters, such as a and g.