I'm a builder that has been teaching framebuilding classes since the middle 70's. There are 2 common approaches to designing a frame. The 1st most commonly used is to design a frame for maximum speed with good handling. If you are young and fit and fast, this is a good approach. However there are many cyclists that have issues (extra weight, loss of flexibility) that prevent them from contorting themselves into a go fast position. For this group, I start the design process by 1st establishing their seat/handlebar/pedal relationship on a stationary adjustable fitting bicycle. For some being comfortable is their primary concern. I have even designed my fixture (laser cut and etched out of stainless steel in Ukraine) to convert a person's position into a frame design. Of course this method probably involves some compromises. To sit a bit more upright might affect handling for example. No matter it becomes the design that works best for that particular individual. The chapters in my framebuilding class manual on proper fit and frame design variable are pages long so I can't very well abbreviate them here. Your teacher Dave should be able to provide insight during your class.