THE idea was never to try to supplant retail, says Fan Bi, the 22-year-old chief executive of Blank Label. Sometimes you need a dress shirt right now, and at those times, Mr. Bi says approvingly, “you can get it right now at Nordstrom.”

But what about those times when you get a hankering not to wear the same thing that 10,000 other men are wearing? Or when you wish you could have the fabric, collar, pockets and lining you’ve always wanted — not what some fashion buyer has chosen for this season? What if you could design that shirt yourself and hang it in your closet for about the same price as a mass-produced button-down?

“The value proposition of customization at retail prices was a cornerstone of our company from the very start,” Mr. Bi tells me by phone from Shanghai, where Blank Label shirts are sewn to customers’ specifications and delivered anywhere in the world in about four weeks. But Blank Label, his Web start-up based in Boston, offers something else that off-the-rack doesn’t: “the emotional value proposition: how expressive something is.”

“People really like a Blank Label shirt because they can say, ‘I had a part in creating this.’ ”

Since last Halloween, when the company’s dress shirt design application made its debut at www.blank-label.com, Mr. Bi and his three partners — ages 19, 22 and 30 — have joined a small but growing co-creation movement that uses the Internet to let consumers have a hand in making the products they buy. Web ventures have already popped up that allow shoppers to customize granola (MeAndGoji.com), jewelry (gemvara.com), chocolate (CreateMyChocolate.com), handbags (LaudiVidni.com) and clothing for girls ages 6 to 12 (FashionPlaytes.com). There are also online competitors selling design-your-own shirts, while Brooks Brothers is one major retailer that offers the service on its Web site.