While blockchain technologies are gaining momentum within supply chains, academic understanding of concrete, real-life design and implementation is still lagging, hence offering very limited insights into the true implications of blockchain technology on supply chains. This paper reports a two-year design science research (DSR) study of a smart contract initiative piloted by a consortium in the UK's construction sector. We seek answers to the research question, 'How should a blockchain enabled supply chain be designed?' Guided by the theory of business model, we explore how a group of supply chain actors collectively designs and pilots a blockchain solution that addresses the supply chain transparency and provenance problem. Our research is one of the very few longitudinal empirical studies to offer in-depth evidence about how blockchain is deployed in complex multi-tier supply chain networks. In compliance with DSR research paradigm, we make contributions at three levels: designing and instantiating the blockchain architect and proving its utility in addressing the target problem; developing a set of design principles as a mid-range theory that can be applied and tested in different blockchain supply chain contexts; and refining and extending the kernel theory of business value at supply chain network level.