Melamine is affordable but prone to "ghosting" over time. Porcelain or Glass surfaces are more durable, easier to clean, and usually come with a longer warranty.
Finding a large dry erase board depends on whether you need a professional-grade office fixture or a budget-friendly DIY solution. You can find them at major office supply stores, big-box retailers, and home improvement centers. Top Retailers for Large Boards
If you plan to use magnets to hold notes or documents, ensure the board specifies a steel or magnetic backing.