A not so simple request - a tool that builds a gun from a few different options, such as type, (Shotgun, Rifle, AR, Grenade Launcher, ETC) And then stuff like stock, receiver, barrel, and magazine. While you modified it, the stats would change for better or worse depending on the part. You could also get a secondary attachment, like a scope, a grenade launcher, shotgun attachment, silencer, laser-sight, etc.
TBH, I don’t even know if it possible. Can you even HAVE sectioned view models in source?