I feel like this every time I do some project around the house. After replacing my toilet a few years ago I realized that manual labor is bad for the knees but good for the soul. But knowing me I would probably end up writing a script to help whatever job I was doing, and then end up making that my focus.
Cut to five years later when your former-plumbing shop is now selling an inventory control PAAS to other plumbers and you're now trying to learn swift so you can port to the latest ipads.
I've had to amend that after a shameful disaster with a half-lap joint beam - "Measure twice, think once, cut once."
Blender and FreeCAD are both good open source options. You can also alternatively draw an SVG in Inkscape, import in to one or the other, then 3D extrude it.
Evidently order is important here. Measuring and cutting are not commutative operations.
Also, if you have two parts to join, the measuring on both sides doesn't cancel.
If only carpentry and woodworking were as easy as algebra.
Allows to make 2D drawing and assemblies etc, even animate joints. It's not open-source unfortunately though.
Example: https://cad.onshape.com/documents/72898c3fef68768a08c1287a/w...
Perhaps you can but for anyone else reading, this is a big and complicated project. Far beyond the capabilities of an enthusiastic/studious beginner. Your mitre saw or cross cut jig/sled being just a few thousanths off will mess this project up. This guy did a really great job.
Trial and Error is all you need. I've never formally trained myself in woodworking and I'm pretty good at it. I could definately replicate what this guy did if I had the time and money. My wife and I have a book collection that currently lives on eight 2.5 metre high by 1 metre wide Oak bookcases that fully line two walls of our living room (which we call the Library). Each unit has 8 shelves (so 64 metres-ish of book space). All built by my fair hand.
The trick is to plan, and to plan well. being able to mock things up in a basic CAD package is a must. I use an old copy of Sketchup (the offline version) and it does me.
After that it's tools. Bad tools make for a bad job. If you can, spend money on good tools, but only buy what you need for that job. After a few years, you'll have a workshop full of nice kit that enables you to tackle anything. Once you learn what your tools can do, you suddenly realise how many projects are now accessible. It's a bit like getting a 3D printer and realising how many things you can now build or fix!
Finally, measure twice and cut once. This is your mantra. Accuracy is everything. If you are not sure, cut the wood slightly too big and trim off until it fits - it's easy to make a bit of wood smaller, it's impossible to make it bigger.
I've also designed, built and fitted our kitchen (that's all Oak also), and the desk units in the study (where I'm typing this) plus numerous other projects to long to list.
If I could give up IT and do woodworking everyday, I would.