Harvest up on high veranda (5)
I believe the answer is:
porch
'veranda' is the definition.
(I've seen this before)
'harvest up on high' is the wordplay.
'harvest' becomes 'crop' (synonyms).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'high' becomes 'h' (abbreviation).
'crop' reversed gives 'porc'.
'porc'+'h'='PORCH'
(Other definitions for porch that I've seen before include "Covered entrance to a building" , "Roofed entrance to house" , "architectural feature" , "Protection over a doorway" , "Sheltered entrance" .)