Day of celebration, perhaps, in flats I've renovated (8)
I believe the answer is:
festival
'day of celebration' is the definition.
(I've seen this before)
'flats i've renovated' is the wordplay.
'renovated' indicates anagramming the letters.
'flats'+'ive'='flatsive'
'flatsive' is an anagram of 'FESTIVAL'.
'perhaps in' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for festival that I've seen before include "Day set aside for celebration" , "Carnival or jamboree" , "Gala" , "Period for feasting and celebration" , "Celebration, religious or artistic" .)