For a lot of businesses it makes sense to build the schedule based on estimated sales for the week. This way you can make sure you are never spending more on labor than you should be. In ZoomShift you can track your labor-to-sales ratio really easily.
If you click Tools -> Labor to Sales Calculator you will see a pop-up like the one below. You can use this pop-up to enter your estimated sales numbers and then see your labor to sales ratio calculated.