You see the terms custom and customization being thrown around and used interchangeably quite a bit in web design and development, especially in WordPress design and development. But, they really don’t mean the same thing. And, you might not need the one you think you do.
First, the front-end display of a WordPress site is determined by the theme you are using. You can get many themes for free, some even better ones that are paid, or you can have one built especially for you. If you or your developer uses a ready-made theme, you will almost certainly want some customization of that theme. You will want the colors to match your branding. You might want to change the font. You will want to add graphics, images, and verbiage that make it your own. And, you will probably need to have some plugins installed and configured to add functionality. Yes, ready-made themes can be used “out of the box” by just adding your content, but most people just are not happy with that, so they need to have their themes customized.
A custom theme is very different. It is a theme built from scratch especially for you. Building a theme from scratch is a lot more work for your developer. You don’t need to change it because it will have been built the way you want it from the beginning. It will take longer and cost more than a customized theme, but it is yours. You can have it exactly like you want it, for the most part. And, you won’t run into anything exactly like yours somewhere else on the internet.
So, what do you need and how do you decide? Many times it boils down to time and budget. If you have the time and money, I would absolutely have a custom site built especially for you. It is more personal, and you can have it the way you like it. But, if you need something fairly quickly and/or don’t have a big budget, you may want to consider a customized theme. While the developer in me would much rather build one from scratch, a customized theme really isn’t a bad thing, especially if you are a new business with limited funds. Look around at sites you like. There is probably an existing theme out there with a similar layout. And, once we customize it with your colors, your logo, your images, and your words, it will seem pretty custom.