Mjecoc

Can some one help me please . I am building a new dwelling (self build) - the new house will be formed from an old stone barn being converted (which is part of a listed building) with a large new build extension (2/3rds of the plot) being built over a stable block which has been completely demolished, as part of the permission, and removed to ground level. My contractor has put his first invoice in with 20% vat, but I think it should either be 0% (as new build) or 5% vat (followed by reclaim at end under self build 431C rules), but not sure , can someone advise please, as I know I need to sort this at the beginning ! Thanks .