Usually people that make there own preworkout sometimes use a cup of black coffee, but they'll also have something like creatine, beta alanine, citrulline malate, and various other things in bulk. Making your own preworkout can save money and make it so you can pick your favorite ingredients and not under dose them like some preworkouts.
If its just coffee and nothing else, I'd choose Pre Workout for sure. If its a cup of black coffee, 5g beta alanine, 5g creapure, and some other goodies than I'm going that route.
Your only as big as your last set. Stop talking about the days that you could push up weight. Live in the now and never stop achieving - My views on lifting and getting tired of hearing people talk about the past and how much they used to be able to put up.