Yep, I've built a bunch of amps. Nothing fancy. Initially went to college to study acoustical engineering. Built my first circuits there for one of my classes. Physics is fun. Math is hard. So I got a business degree instead and have a successful career as a creative in advertising. Started building a few kits here and there for fun, then looked at schematics online and built variations of whatever looked interesting. Modded Marshalls, SLOs, Bogners, Jose mods, etc. I learn as much as I can and have fun building the occasional amp. I can certainly build a wicked mean and pissed-off 800/Jose, but it's nothing I claim I personally designed because I did not invent the JCM800 or Jose mod. But I've certainly re-voiced the design to my personal preferences.
Once you learn what each part of a circuit does, you can start tweaking things and re-voicing things however you want. But it's my opinion that changing the voicing of a pre-existing circuit does not mean you invented something new. It's like finding a recipe for cake on the internet and then experimenting the ingredient amounts. You didn't invent that kind of cake. You simply added more sugar, used 3 eggs instead of 4, and baked it in a water bath at 350 degrees instead of 300. All this drama around guitar amps is similar.
I've had a few offers from some well-known companies and boutique builders to work for them building amps, but it never seemed worth the headache.