Comparing the areas, shadowing and footprint of different scenarios is a key part of design. Giraffe supports it with layers.
1. Create draw layers in the layer menu. The active layer button controls which layer all geometry will be created on.
2. Areas are calculated only on layers that are active.
3. Geometries on different layers don't stack!
4. Layers can be used in the normal view and also in the 3D view.
Video to explain it all: