First would be 3 - 6 coats of magnetic paint (I know, right? Who knew?)
Potential drawbacks: the iron flakes in the paint produce a not so smooth finish. Not a problem unless I also wanted the same board to be a chalkboard:
And I might be able to mix up my own color?
Making my own dry erase board is also an option:
Using any of these methods, or a combination there of would let me create my own original and uniquely shaped planning board. However, too many coats on top of the magnetic paint dilutes its already meager magnetic properties:
Thick Steel Plate 6.44 lb
Refrigerator Door 3.40 lb
Magnetic Paint, 3 coats 0.25 lb
Magnetic Paint, 6 coats 0.52 lb
Then there is always the option of buying a steel plate, and painting part of it for chalkboard and part for dry erase. Or buying a magnetic dry erase board and painting part of it as a chalk board. And of course, then there are the choices of dry erase pens, real chalk, or liquid chalk pens (which also write on dry erase boards).
So many options - and all the time in the world to decide.