From a professional stand point, there is may concerns in using a drone system and you need to ask a boat load of questions before investing. Creating as built condition has many factors for example what is the final deliverable, what tolerances are exceptable, is the area populated, what are my restrictions, is the client looking for building structures or GIS information, and the list goes on depending the client.
From a LS stand point can the results of your replicated by conventional means to help support your findings? There is a business model that supports using drones but you also need to have back office support to put together the information together that can QA/QC before the client receive the information.
If your heart desires is to continue, I would suggest to start collecting information on how to properly create as built condition of dirt and stone piles for volume calculations.