Will comment later.
EDIT MARCH 4th:
Finally got to a computer.
I did this at 2AM on the morning of the 14th. I had been kicking the idea around in my head for about a month prior, and was insanely stoked that I actually went through with it.
For the base layer of white I used children's poster paint, applied with a paint roller.
The roses are each about 5 and a half feet tall, and yeah, there's a dozen of them. The 12 of them fit better than I thought they would.
It was visible all Valentine's Day, then covered up on the morning of the 15th.