It’s not that difficult to find plans available either for free or for sale on the internet, though I have yet to build a furniture project straight from plans. I’ll usually come up with something I want to build, and I’ll look at pictures, watch build videos, maybe find plans, and then I’ll design my own version in FreeCAD.

I tend to start in the spreadsheet workbench and list things like stock dimensions, pertinent detail dimensions and such, derive certain dimensions, I like to keep as much math in the spreadsheet as possible, and then I use the sketch > Part Design workflow to create the parts and the A2Plus workbench to assemble them. Creating a 3D model is often a sanity check to make sure all the parts fit together, I sometimes don’t bother to model all parts or I’ll only do half of a symmetrical assembly. I used to make drawings to print with the TechDraw workbench but for my purposes in the shop I stopped doing this as I would just work from the spreadsheet. If I was sharing my plans with others I would make more careful drawings.

This of course allows you to tailor the work to your space and you.