I will be having a building lot 3D scanned due to its topography.
What would be the easiest/most efficient output file format that I should ask for in order to model the lot in Sketchup without using paid extensions (if at all needed)?
If the software used can fit a surface to the scan and output that to DWG or IFC it would be perhaps the best solution. If they can generate 3D contours at a decent interval for you and make a DWG that would also be good, you can use the Sandbox from Contours tool to fit in the surface in SketchUp.