chalkboard paint (There are varieties of colors to choose from or you can even mix your own color at Home Depot. We used 2 cans of Rust-Oleum Specialty 30-oz Flat Chalkboard Paint in Charcoal Gray), paint brushes, rollers, roller tray, painter's tape, tarp or newspaper, primer
Step One: layout a tarp or newspaper on the floor under the door and around.
Step Two: prepare the surface -- if unpainted, it needs a coat of primer. Or if it is already painted (most likely), clean it completely, then lightly sand down any protruding imperfections and smooth out the surface. (I forgot to tell Bill to to lightly sand and he ended up completely sanding down the white paint of the door. He ended up with sore arms.) Clean off the dust from sanding, and let dry completely.
Step Three: tape off the door edges with painter's tape.
Step Four: apply the chalkboard paint with a brush or roller. (Bill used medium and large size rollers) Let the coat dry for a day, then if needed then apply a second coat. For us this was just right. The extra coat(s) ensures a thick and durable chalk surface.
Step Five: allow the painted area to cure for 3 days before using it as a chalkboard. Then, prior to initial use, rub the entire surface with the side of a piece of white chalk, then lightly erase it all.
I love large chalk better than the thin because it tends to be more soft and goes on smoothly. And for the eraser you can purchase one at an office supply store or use a damp towel. Damp towel works great if you don't want dusts to go all over the place. Let me know how it goes!