OP's friend needs a store quickly, and probably wants a stable, feature-rich, ready to use store. OP most likely does not want to get blind-sided discovering that the plethora of currently existing solutions have upwards of well over $1 million dollars of labor-hours (features, QA, documentation) put into them. Magento might even have over $1 billion in labor-hours. Rolling your own out of simple ignorance regarding what exists is already rather dumb, but the surprise finding out that making anything worth using is a full-time job will be soul crushing, depressing, and may even damage OP's relationship.

Writing an ecommerce CMS because you are educated on what exists and want to innovate is a completely different matter.