The roof has two coats of blackboard paint and it's looking good. But I think I'll add just one more coat.
The paint instructions call for one coat of paint to be applied in one direction and the second to be applied at right angles. Which I did. But I applied the first coat vertically and the second horizontally. I should have done it horizontally, then vertically. That's why I decided to do a third coat vertically. It just works better.
The trick to doing those three coats is:
a paint tray like this which is sealable during coats:
Don't know where I got it but it's about 4" x 3" x 1" and the bottom is marked PLACON CS04 (made with ECOSTAT Recycled PET).
I used a 2" foam brush that I wrapped in saran wrap immediately after painting each coat.