Anyone can build a website, but not everyone can design a website. There are several services that anyone can subscribe to and build a website from a pre-defined template that is available to all the other subscribers. You can change the look by modifying the colors, typeface and images. But, you still have a template that someone else is using also.
A website built by a web professional can make your brand stand out from all of the sites built with templates, like those cookie cutter design that are prevalent on the web. Stand out and have your content presented in a unique way. By having a web designer advise you on the structure and components of your website, they can help you get your business or organizations message across with a professional, modern look.