You can make your own dry erase board like this https://www.hometalk.com/34419905/upcycle-an-old-frame-and-some-corks-into-a-diy-dry-erase-board or a magnetic board like this https://www.hometalk.com/18534477/huge-colorful-magnetic-board

Upcycle An Old Frame And Some Corks Into A DIY Dry Erase Board

Huge Colorful Magnetic Board

A cheap piece of sheet metal can be used as a base and a wooden frame around it to dress it up was my first thought. They sell dry-erase paint that would cover the sheet metal. There also are metal paints that can be put on any surface to allow magnets to stick.

Caroline: Sometimes, it's easier/cheaper! just to buy than to DYI... here's a rather large one:

https://www.walmart.com/ip/Quartet-Magnetic-Dry-Erase-Board-Tile-14-x-14-Frameless-Assorted-Colors-85402-WM/17163547

there was at one time blackboard paint that would go over metal.

They make magnetic paint you can make your own on any wall or piece of wall board.... https://www.youtube.com/watch?v=aCZHQw-wJ_Y they sell this at True Value hardware store, lowes, home depot and walmart

Ophs wrong link, hate when that happens.... https://www.amazon.com/Rust-Oleum-247596-Magnetic-Primer-30/dp/B003ZW7XL4/ref=asc_df_B003ZW7XL4/?tag=hyprod-20&linkCode=df0&hvadid=216743026518&hvpos=1o2&hvnetw=g&hvrand=3096576008885096502&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9033057&hvtargid=pla-392662394041&psc=1