Is it insulated? Check the ceiling insulation and don’t always rely on your builder’s opinion of the insulation. Insulation should be around 200mm thick and ideally covering the joists to create a good thermal barrier – “it’s got batts” does not always mean it’s suitably insulated. Insulation should exceed building code, where possible, in the floor and ceiling.
Where will the sun be in winter? Check the WCC solar radiation map to see how much sun light the home will get. Take note of the trees, houses and banks that may block valuable sun light. Kiwibank also have a free sun tracker app for home buyers.
Is there damp proofing? If the home has a suspended wooden floor check to see if there is a polythene barrier to stop the damper air rising up into the home. Survey around the perimeter of the home to note any places where water could run off or soak under the house from banks. Would a field drain help redirect water from elevated areas?
Is there heating? Have a look around for a fixed method of heating. Heat pumps or wood burners will provide reasonable bills. Remember just heating the lounge will often not be enough. You should consider installing fixed heating to service bedrooms also.