This is the step where everything comes together. It is time to design the architecture of your computer. The architecture is how the registers and different components of your computer are organized. The design aspect is completely up to you, although it helps to keep a goal in mind (what you want your computer to do) and a model to go off of. If you want to design your computer after mine it is completely fine. I modified the architecture of the SAP-1 found in Digital Computer Electronics for my 8-bit computer.
One design aspect to always keep in mind is how data is transferred between the various components of your computer. The most common method is to have a common "bus" for all of the data on the computer. The inputs and outputs of the registers, ALU, program counter and RAM all are connected to the computer's bus. The wires are arranged in order from least significant bit (1) to highest significant bit (128).
Any and all outputs that are connected to the bus have to be completely disconnected while inactive or else they would merge with each other and result in erroneous output. To do this we use Tri-state buffers to control the output of certain elements that output by default like the accumulator, ALU and actual input for the programming of the computer.