"A new architect will come to the agency tomorrow."
Translation:Un nouvel architecte viendra à l'agence demain.
Nouvel, rather than nouveau, is used just for smooth pronunciation purposes which happens when the adjective comes before a noun that starts with a vowel or H.
Mind you, the feminine is actually nouvelle and nouveaux will be used for plural.
Another example is mon amie. Here, amie is clearly feminine but you still use mon to effect a smooth pronunciation.