I've had a magnet board on the wall above my bed for a while now, but it quickly became too small for all the lovely postcards that I got. Therefore, I have been looking for a bigger one, albeit without luck.
However, on one of my strolls through my father's basement (where tons of stuff from my childhood is stored) I came across our old chalk board. I've always thought that this was some children's toy chalk board, but my father actually brought it home from work one day after they switched to more modern ones :D (Yay for the 80s!)
Anyway, the chalk board had the perfect size for the space above my bed, so I decided to turn it into a magnet board.
I bought a 2,5l-bucket of magnetic paint; the board is 1m*1,3m, and the paint lasted for seven layers. I'd read a lot of reviews for magnetic paint and a lot of people complained that their magnets wouldn't stick. I've bought super powerful ones that hold my postcards just fine. The red magnets are "normal" ones that do stick as well but not as safely.
My recommendation is: Use at least seven or eight layers of magnetic paint and buy strong magnets, especially if you want to put thicker/heavier stuff than postcards on the board.