Have you looked at Ana Whites website? She has some fabulous designs. Attaching a link here, if this is not exactly what you want have a look around other options on website there’s usually multiple different styles.
So many options depending on how big,seating or not,movable etc.. here's bunch DIY builds https://www.youtube.com/results?search_query=DIY+kitchen+islands or from repurposed furniture https://www.youtube.com/results?search_query=diy+kitchen+island+from+dresser
Here are some tutorials on how to build a kitchen island on Hometalk: https://www.hometalk.com/search/posts?filter=build%20a%20kitchen%20island
Really depends on what you want, we made one out of new cabinets then added a counter top. But I've seen where people make them out of a 2 x 4 frame then close them in with shelves.
First figure out what you want then go from there.