[aixguy]

First off, if you are planning on painting a big mural, like 4x4 you will be better off with paint burshes. An airbursh has a spray width of about 1" round. Mural guys use brushes, rollers, big spray guns and then the air brush for the detail at the end of the job.
Painting block with a roller is a pia, I would put up ferring strips and drywall or launa, prime then do your art work.
Good luck!