Builders finish is usually the shell … ie plastered walls (not painted) and concrete floors (not wooden / carpeted). The fascia and soffitshould be part of this deal, but as to the material spec that should have been agreed before he got the job! Most fascia and soffit is now UPVC, but I have seen some to go yellow after 4/5 years. I would recommend MFP myself although it can be a few quid more.