If a company is supplying services relating to new builds, then if all conditions are met as per VAT notice 708 section 3, the supply is zero-rated.
Buildings and construction (VAT Notice 708)
The company would not charge VAT on their invoices if one of the properties is for the plot owner to use for himself to live in. He would have to have invoices made out to him, as the claimant, to recover the VAT on materials he purchases himself to claim under the DIY new builders scheme.
Claim a VAT refund if you build new houses on a DIY basis
The construction company would recover the VAT they incur on the materials under normal input tax rules.