If you're someone who likes that extra level of control in your nutrition and supplementation, there's no reason you couldn't make your own pre-workout. Well, scratch that, there are a couple of reasons: It can end up being far more expensive, and depending on how you make it, you might miss out on a few key ingredients. And the taste is probably going to be terrible… Yeah, this is a pretty tall order for the average gym-goer.
So, before you put on a lab coat and go deep into PubMed, make sure you have a rock-solid foundation of training and nutrition. Are you training 3-5 times a week consistently, and with good form? Are you eating adequate calories and protein, and having a solid pre-workout meal before intense training sessions? Check, check, check. OK, then maybe you're no longer an "average" gym-goer.
That said, before you start perusing the dark web for a discounted palette of pure African yohimbine, bear in mind that starting simple is almost always the best option. If you're going to make your own pre, keep it to the key ingredients that the best pre-workouts share: caffeine (if that's your thing), beta-alanine, and perhaps nitric oxide boosters for endurance and pumps. If you want to go down the rabbit hole of nootropics (i.e., brain-boosting supplements) or other highly goal-specific ingredients, go for it—but don't expect magic.
Remember, this isn't about cheating the process. It's only about reasonably enhancing what you can get out of it!