You would build your own website with a retail store online if your intention is to sell the website, address and all, as a commercial real estate investment that could pay off down the road. If it is tied to your company, it would be a good idea. If you use Ebay.com, you are selling to Ebay customers. It’s a good option for selling things, but not for building a piece of commercial real estate. It’s as though you were leasing the land, but without the land, you have no asset. You can’t sell that later.
An Ebay store is a way to capture a portion of customer traffic and make money right there from sales on Ebay. But the long term benefit of Ebay is when you can drive that traffic to your own website after the sale by promising better prices at your own website. Now, there is one complication. Ebay does not allow you to offer a link or direct pitch to your own website. So, you have to include a flyer when you mail the product to the customer that then advertises your own website.
All that being said, if you have the energy, you could do both. Put a post card in every Ebay shipment advertising your own website. That’s okay with the Ebay rules. On your own site, maybe the prices are better and you have a lot more merchandise. Ebay is a great place to start building traffic if you are building your own piece of web real estate.