Using QGIS 3.4, I am trying to merge multiple DEMs downloaded from the National Map Viewer that are in ArcGRID format (Arc/Info Binary Grid). The output will be a large file so I can't use any of the formats limited to 2 or 4GB in size. I would like to save it as a BigTIFF but I don't know how to distinguish that from a TIFF in the merge raster dialogue box. I tried to save it as TIFF but it failed as file was over 4GB.
How do I save merged rasters as BigTIFF or, if this is not possible, how do I merge rasters to produce the smallest possible file size?