I sometimes browse the brewdog catalogue for ideas and then add my own tweaks. Since your friends want to learn, I’d say do something simple for this. One of my early experiments was based on their skull candy. For making things interesting, fermenting with kveik is pretty fun and surprisingly fast. That yeast is a monster. I like the Opshaug kveik, it results in a pretty clean and fruity flavor. Note that kveik needs pretty high temperatures.