Very big chaps breaking into dilapidated semi (7)
I believe the answer is:
immense
'very big' is the definition.
(immense can mean massive)
'chaps breaking into dilapidated semi' is the wordplay.
'chaps' becomes 'men' (chap means a man).
'breaking into' indicates putting letters inside.
'dilapidated' indicates an anagram.
'semi' is an anagram of 'imse'.
'men' going into 'imse' is 'IMMENSE'.
(Other definitions for immense that I've seen before include "Mammoth" , "Very big, exceedingly great" , "Exceedingly large" , "'Vast, colossal (7)'" , "Extremely large or great" .)