My first 3pc build, I tried to blue print a design (as best I could), that I knew was a great shooting and solid design. After that first build, I learned some things, and refined my design to follow function. The characteristics of the grip and and my preference of the blending between that shape, the sight window, the limb pads, the blending of the limbs into the riser, and sometimes the materials being used, dictate the end design of the bow.
This has worked best for me when designing a riser around a known limb design. If designing a new limb, I like to get a new form worked out, figure out the best limb pad angle and riser length, then repeat the above process. For me, form follows function, then your artistic creativity works to make a good looking bow.