Dad converted one with difficulty into an extra room (8)
I believe the answer is:
addition
'an extra room' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe there's an association between them I don't understand?
'dad converted one with difficulty into' is the wordplay.
'converted' indicates an anagram.
'one' becomes 'i' (Roman numeral).
'with difficulty' indicates anagramming the letters.
'dad' is an anagram of 'add'.
'into' is an anagram of 'tion'.
'add'+'i'+'tion'='ADDITION'
Can you help me to learn more?
(Other definitions for addition that I've seen before include "Summing up process?" , "an arithmetical process" , "Calculation of the sum of two or more" , "Arithmetic calculation" , "Simple kind of arithmetic" .)