The most common and most likely answer to this crossword clue is the 3 plus 5 plus 2 plus 5 letter word THE TOWER OF BABEL
I've seen this crossword clue in Financial Times
T
H
E
T
O
W
E
R
O
F
B
A
B
E
L
Buddy explains!
The straight part
We know that "tall building" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case tall building = the tower of babel.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.