Virtual reality applications are being designed and used for training in different fields, such as medicine, emergency response and exercise. Here, we show how we created a cognitive training tool using Unity3d and the Oculus Rift head-mounted display from a strong, dedicated design and planning phase before software implementation. First, in a conception phase, a research was done to understand how to do game development and cognitive training, then we made a paper prototype integrating the findings. Later, in the implementation phase the scene was set up as well as the interface with the head-mounted display, and finally the gameplay elements were programmed in. This resulted in a training tool that was later run through usability tests.