Visual Studio 2017 has a brand-new lightweight and modular installer. The installer breaks Visual Studio down into independent workloads that allow you to install just what you need, helping you get to coding much faster. For example, the Universal Windows Platform development workload gives you the right tools to be productive in authoring, debugging, and publishing UWP apps. If something is missing, you will be able to add it later using the Visual Studio Installer.
Visual Studio MVP Kent Bryant shares the installation size of different Visual Studio 2017 Workloads in this blog post.
The minimum installation size, if you just install the Visual Studio Core Editor, is 600MB. And if you select everything to install, the max installation size is 82.58GB.