Yes and no, it all depends on your preferences.

Yes, if you want to put your own design on your website and No if you’re fine with free and pre-installed evoskins and if you want to download additional skins from the b2evolution Skin Directory.

Even, if you’ve decided to use a pre-installed or downloaded design, you can still customize the design to your own taste and preference. It’s perfectly normal to want to personalize the look of your blog to match your personality or your blog’s theme.

If you really wanted to provide your own design, and depending on your knowledge and skills, you can create your own skin from scratch or integrate b2evolution on an existing website with an existing design.