Setbacks require a site boundary to exist. To create setbacks, first you’ll need to set the height reference point - this is effectively the average grade location for your site. It is the point on your site at which the setback height will be applied from.
Select your site. You’ll see a Site Boundary sidebar on the right with a Set height reference point to enable setbacks button. Click the button.
Next, follow the prompt and click somewhere on your site to set the height reference point location. When you’re done with placement click the checkmark button to continue.
After clicking the checkmark button you’ll see a new Setbacks section appear. Click the + button in that section to add a new setback.
Setbacks can be given a distance per side as well as a height. You can press Tab to cycle through the side dimensions, click on the particular side dimension you want to edit, or enter a value into the Distance input in the right sidebar to set all sides to the same value.
When you’re done, press the X in the right sidebar to deselect the setback.
Repeat the steps above to create as many setbacks as needed.
The Opacity input in the Envelope section of the Site Boundary sidebar lets you change the visibility of the site envelope/setbacks.
