When you start a new project how will you manage the requirments and specifications?

I start my new project in 2015 to 2016 that's  my final year project my project is Vehicle speedo meter controlling speed by android mobile I used sensors , stepper motors and some more equipment's to achieve my goals  

Before project Start Up, detailed plans, specifications, requirements should be set up, it should be depends with the Project Manager on which system he should be comfortable to use, either Primavera P6, MS Project, Excel as long as the Planned Schedules or project requirements are all determined, WBS are already determined,  like Milestone, manpower requirements, materials procurement and delivery. But once the project had already started, then that should be the time where in you can determined other materials needed, delays due to climate, risk, change orders, delays on deliveries, material sourcing, and all other factors that you will may encounter during the project execution.

In a project requirements & specifications are understood and planned before formal commencement of a project. How ever few requirements are thrown together and such requirements & specifications occur only after start of the project.  

Similarly in construction projects complete requirements & specifications are understood, planned and scheduled before commencement of project and based on that the project is started and executed, but few requirements like minor changes in design, delay in payments, design issues, change in material specification, etc are such requirements that occur only after start of the project, and have to be managed accordingly.