Ultra high-performance concrete (UHPC) is a relatively new concrete material that is high in strength and durability. Its high quality typically comes at the price of high material costs, high carbon footprint and low production efficiency. The objective of this paper is to explore the design process for developing an economical base mix of UHPC that can be used for a wide array of precast building applications. Taking an iterative approach, various materials were tried and tested, measuring the hardened and fresh properties of the resulting UHPC. This paper discusses the use of particle packing, and cement and sand selection to optimize the mixing time, workability and strength of category 120 UHPC. While a particle packing model is a good starting point for developing a UHPC mix, other factors that needed to be considered were the chemical compositions of selected materials and the sizes and shapes of particles. The overall distribution of particles had the biggest impact on the overall quality of UHPC. The shapes of particles affected the consistency between UHPC samples. Factors affecting the workability and early age strength of UHPC were directly related to the rate of hydration, while the size and distribution of particles affected the magnitude of mixing energy required.