Working with your Architect in selecting the correct materials and sourcing any finishes and fittings yourself as the builder will likely add a mark-up. Likewise with kitchens, sourcing them via a supplier directly will save on costs as you can shop around for the best deals. Another route is to order the kitchen units yourselves and have it arrive flat packed for either you or your builder to install - just be careful with taking the correct measurements as it'll be your responsibility if they are incorrect.