The most common and most likely answer to this crossword clue is the 11 letter word SPLIT-LEVEL
I've seen this crossword clue in The Guardian
S
P
L
I
T
-
L
E
V
E
L
Buddy explains!
The straight part
We know that "with floors at different heights" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case with floors at different heights = split-level.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 SPLIT-LEVEL mean?
SPLIT-LEVEL noun- A building of this kind.
- Of a building: built with rooms on levels separated by stairs of less than a full storey.