The most common and most likely answer to this crossword clue is the 10 letter word SPLIT-LEVE
I've seen this crossword clue in The Guardian
S
P
L
I
T
-
L
E
V
E
Buddy explains!
The straight part
We know that "sort of flat?/sort of flat?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sort of flat?/sort of flat? = split-leve.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.