Short Answer: Use Scan to mesh function in recap. My preferred method. Trace geometry over the point cloud with CAD or BIM software.
Long Answer: scanning a building can result in an enormous amount of information. Point clouds were conceived as a way of making it more manageable. A pointcloud is made up of (as the name suggests) a large number of individual, disconnected points in space which together can give you an idea of the scanned object.. Step and iges files describe closed objects and surfaces. In order to get your point cloud into one of those formats you need some software that will trace over those points with surfaces or solids. YOu can do it manually or use recap's scan-to-mesh function which will attempt to create a mesh or continuous surface that loosely describes your point cloud. However, this can result in files that are too large to load. IF you are going this route delete as much as you can from the point cloud and break up the conversion into small and manageable pieces.
