For me, there are two answers. One is reality and one is my dream. Reality, I probably build a new one every decade because I can’t afford to buy all of the parts at once. At best, I upgrade a part here and there every 4-5 years depending on if I can afford it.
The dream, though, is a major upgrade or entirely new build every couple of years at most. That would be amazing, but it’s impossible! Unless I ever win one of these contests. 😆