As already pointed out by Steven Ventimiglia there is not pointing of developing an e-commerce site from scratch as it will consume a lot of time and will be no where close to FREE / lightly paid solutions available in market which are more robust, easy to use and secure.
If you are an organisation you can develop site for your own custom requirement however, if you are individual you can better opt for solutions such as ( OpenCart, PrestaShop ) or SaaS hosted solutions likes ( Shopify ) .
Atul Sharma
Full Stack Developer | Cloud Native Applications