Good engineers finally made home most eco-friendly (8)
I believe the answer is:
greenest
'most eco-friendly' is the definition.
'good engineers finally made home' is the wordplay.
'good' becomes 'g' (abbreviation).
'engineers' becomes 're' (Royal Engineers).
'finally' says to take the final letters.
'home' becomes 'nest' (a bird's home).
The final letter of 'made' is 'e'.
'g'+'re'+'e'+'nest'='GREENEST'
(Other definitions for greenest that I've seen before include "Most unsophisticated" , "Extremely immature" , "Most naive" , "Most verdant" .)