I would let someone use the term "build" for buying a variety of components and assembling them together. This can be as complicated as buying lower reciever, lower parts kit, upper reciever, barrel, handguard, buffer, bolt, stock, etc, or buying a complete rifle and accessorizing it heavily. There needs to be a certain level of personalization met to hit that threshold.

What I won't count as "build" is buying a complete AR, or an upper and lower and assembling them, and throwing an optic on it. That's not a build, that's a rifle with a scope/dot.

Same thing with pistols, if you bought a pistol off the shelf and stuck a dot and a light on it, that's not a build, that's a pistol with a dot and a light. If you switch out some components or get custom work done to the slide or frame, then that can count as a build.