The most common and most likely answer to this crossword clue is the 3 plus 5 plus 7 letter word SIR EDWIN LUTYENS
I've seen this crossword clue in Financial Times
S
I
R
E
D
W
I
N
L
U
T
Y
E
N
S
Buddy explains!
The straight part
We know that "Architect" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case architect = sir edwin lutyens.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.