Hi there! There are so many really great ideas out there based on what your style is. Some people use old furniture, so people use traditional cabinet bases. I made one out of an old pine table. Here's a link you can peek at: https://www.exquisitelyunremarkable.com/2013/06/decorating-cheats-farmhouse-table.html
You can convert a dresser by removing the mirror.
We have a white cabinet with butcher block top as an island.
My uncle took a table, cut a piece out of it and placed the stove in the cut out so that it looks like the table was built around it. I always that it was so cool that you could leave food on the stove and serve from their.
We built ours beginning with a 2 x 4 frame then then closed in with wood. If you plan to go with a stationary island you could also purchase already made cabinets and then add the counter top of your choice.
We made ours from a TV/entertainment cabinet I found on craigslist for $40. I knew it would be prefect with the deep drawers and shelves plus it was the right length for our kitchen. My husband took the back with the hole cutout off and replaced it with beadboard, cut the legs off and added new legs and built a shelf at the bottom, then put casters on so I can move it around. I stripped the top and stained it, then painted the whole thing bright white and sprayed the drawer handles brushed nickel. Added 2 cute shelves at the sides for spices and bottles and 3 baskets on the bottom shelf. Now we have a beautiful, functional, custom made island for less than $100.