Fusion 360 is a great 3D CAD software that is free for education and hobbyist use. Check out this video and follow along with the files to take your 3D designs from Fusion 360 and cut them out on your Glowforge laser.
If you upload the Fusion 360 Box file it is fully parametric so you can modify the dimensions and number of tabs to any measurements and everything will automatically update. This includes the material thickness.
There are a lot of great box generator websites out there if you want easy laser cut boxes like Boxes.py. This tutorial is to demonstrate my way of exporting any 3D files from Fusion 360 with the intention of laser cutting them. Here are the .svg files for the box above. It is .12" thick with a .25mm offset for a tight fit.