The basic island is built with base cabinets and secured to the floor. You could use drawer or shelf bases or sink/stove base depending on your needs. Any combination of sizes, styles and features that meets your needs. The tops are simply countertops and can be easily fabricated from prefabricated butcherblock, laminate or stone tile on a 3/4" plywood substrate. Its fairly easy, and you could post more specific questions as you progress. So the place to start is by looking at cabinets that meet your style and size requirements.