Readily available materials and those that are most recognisable by the majority of builders. I.e. the more 'bespoke' you go, the more likely to increase the material cost and also reduce the number of builders that are comfortable working with certain materials or construction techniques, and therefore limiting options when tendering the project. You may be able to reuse or reclaim materials from your own demolition or from other projects locally. These could be used to match any new areas of brickwork to the existing, crushed and used as sub-base for a new floor or even within any garden landscaping.