There are a number of ways you can use groups for measuring – what specifically are you looking for or wanting?
Using Takeoff_Length (free with Estimator), you can collect length data in collections (e.g. ridge vent, gutters, hips, etc.) which creates GROUPS for each collection – you can then add cost data per lineal unit you desire.
Using Profile Builder 2: you can create profiles and extrude them to create geometry (like lumber or trim, etc.) – this creates a GROUP and when put on a Layer, cost data may be assigned per lineal unit of your choice.
Does this help? Please advise as to how else we can help make it work best for you. Please feel free to email me directly at firstname.lastname@example.org and I will be glad to help in any way I can.