my experience
I started flight training three and a half years ago and building shortly afterwards. (Of course, family and work have remained present and needed attention as well!) These are both time intensive and exacting pursuits. I found that building definitely took time away from training, and as a result, my flight training has taken longer, been harder, has consumed more hours, and been more expensive, than if I had done it sequentially, instead of in parallel. I joke that the thing that has been the biggest obstacle to me in finding time to train, has been an airplane, ironically.
At your age, if you were to get your private license first, I think you would be better off. My opinion anyway.
I think in my own case, since I did not have experience to guide some of the build decisions, I put more $ into the project than I might have if I had more flying time, and had better defined preferences.
On the other hand, my plane turned out beautifully, and my check ride is coming up...