Here's a pretty one! https://www.hometalk.com/8643449/from-buffet-to-rustic-kitchen-island
This project may give you some ideas.
Ooh that would be so fun. If the buffet is sturdy enough you could top it with a piece of granite or marble. Butcher block would be another great option. You could extend the top over to create a breakfast bar. And you might want to cover the back of the buffet with a nice piece of 1/4" plywood to pretty it up.
ideas videos https://www.youtube.com/results?search_query=diy+buffet+into+kitchen+island
Purchase an inexpensive IKEA top for about $25.00. Mine is black and is 5 foot x 30 inches and they also sell larger ones so you can have seating if you desire. They come in a few colors. I put a black one on top of an old buffet and bought two inexpensive shelf holders to attach it. You can do everything on the top except nothing hot ... use a bread board or trivet. It looks fabulous and can't be easier to keep clean. I think they are in the table top area at IKEA. Inexpensive and good looking!