As long as the end user assembles 51% of it, you don't need it. You self-attest that the device is in compliance. You also have to perform an "RF study" but there is no requirement for documentation on that.

Even in Germany, hams are allowed to build their own transceivers. I can't imagine the FCC being more strict than that.

Yes, the whole point of having a ham license is the permission to build and use your own equipment.

The compromise vs "buy some spectrum for 8 trillion dollars" is that you can't use ham radio for commercial (or musical) purposes.

Heh, ask 10 hams what the whole point of a ham license is and you'll get 10 different answers. I've heard "permission to build" before, but rarely.

Don't have my license yet, but for me it's definitely building homebrew (i.e. designed by me) transceivers. Not actually that interested in talking to other hams except for then testing my gear.

Heh, I'm not that interested in talking, but I am interested in typing. Especially with the advantage of advanced math/error correction, store and forward, relaying, and related. This adds up to a few watts in a $100 radio getting across a country.

Not sure if you mean building or designing and building. But QRP labs has some nice kits.

I'm an aspiring ham myself :D For me, I'm interested in emergency communications, others in the club are DXers... truly fascinating.

It's a ham project, you self-certify. Part 97 allows you to build your own equipment.

Now, in doing so, you're also taking responsibility for your emissions, and you're expected to be diligent about making sure everything is within the rules. But there's no paperwork or anything unless you want there to be. (Taking notes about your spectral purity testing is probably a good idea, you'll probably never need them, but if someone complains it'll be nice to have.)

The nice part of DIY ham stuff is that you don't, you can sell a kit without any issue.