Hi, Thanks for reaching out to us with your query. GST registration is mandatory for getting registered as a seller on Amazon/Flipkart. However it is not necessary that you must have a shop/office space to get your GST certificate. You can register from your home by submitting the proof either in your name of taking NOC from the owner. 
Hope this will help you in setting up your shop on Amazon. If you have any further query, you can write to us at [email protected]