Buy an original retail DVD from a reputable seller. It costs $15–$30, works on any compatible Intel Mac, and provides a clean, untampered installation.
To download , you must distinguish between the full retail installer (needed for a fresh install) and the 10.6.8 Combo Update (used to update an existing Snow Leopard installation). Official & Safe Download Options
Once you have downloaded the DMG file, you can’t just drag it to a thumb drive. You need to "restore" it to make it bootable. Open Disk Utility . Plug in a USB drive (8GB or larger).
If Google Drive displays a "Quota Exceeded" or "Download Limit" message, try creating a copy of the file in your own Google Drive account (Right-click > Make a copy) and then download it from there. Alternatively, use the "Add to My Drive" feature.