Good eggs coming up road rebuilt for scientist (8)
I believe the answer is:
avogadro
'for scientist' is the definition.
(scientist Amedeo Avogadro)
'good eggs coming up road rebuilt' is the wordplay.
'good' becomes 'g' (abbreviation).
'eggs' becomes 'ova' (term for egg cells).
'coming up' is a reversal indicator.
'rebuilt' is an anagram indicator.
'g'+'ova'='gova'
'gova' reversed gives 'avog'.
'road' anagrammed gives 'adro'.
'avog'+'adro'='AVOGADRO'
(Other definitions for avogadro that I've seen before include "scientist" , "Italian physicist giving name to a constant" , "Italian gas physicist" .)