Find a font you like on dafont.com, print it out in a big font (such as one letter per page), use that to create a template, paint/spray away.
Or if you want it bigger, try this: homokaasu.org/rasterbator/
( G/PP 💩💩💩💩💩&#128, Thu 15 Sep 2011, 15:15, archived)

kinda slick.
I was anticipating using sponge printing, with 1.5 inch squares.

A friend of did their kids room head to toe as super mario world, fricking awesome. Couldn't ever manage that, but a name would be good.
( RocketSurgeon is pretending he's still young, Thu 15 Sep 2011, 15:20, archived)

Or ask someone who works for a printing company that do wide format work.
Send them the picture and ask them to print it.
( MONO!, Thu 15 Sep 2011, 15:42, archived)