If he's just a carpenter, it would mean he needs you to be the registered owner builder because he wouldn't have the licensing to be a fully qualified builder (who is then legally allowed and insured to employ other tradies). By becoming the owner builder, the buck stops with you. You have to sign it all off and you are accepting some of the responsibilities of the job. So a bit of a concern if something does go wrong. Are you sure of the licensing and quality of the trades he uses? Are the electrician and plumber licenced? Everyone's insurances up to date? Are you prepared to organise your council inspections? Go for permits etc? That's your responsibility as the owner builder.

We've talked about being owner builder but the only reason we would do that is we know a lot of trades, (DH is a tradie), we understand the building process and the overall builder/carpenter is DH's best friend.

The other thing is if you're going to a bank to have it financed, you'll be looked at less favourably if you're owner builder than if you employ a builder.

The position of owner builder IMO requires some experience, to understand the legalities of it all.