These instructions should get you started using OnShape for designing your own enclosure (for 3D printing or laser cutting). If you are already familiar with and planning to use another CAD tool (such as Fusion 360 or SolidWorks), I would still advise you read through the tutorial below to ensure you are utilizing all the features described (such as setting up variables, mirroring features) – you are free to use whatever CAD software you want (and don’t need to use OnShape).
Why OnShape?
Sign up for a free OnShape education account here: https://www.onshape.com/en/education/sign-up
Follow along with this tutorial
https://www.youtube.com/watch?v=rzscuKC8U_M
The measure tool will help you quickly measure items without having to go into the sketch:
If you’re laser cutting from Design Center