My sister and I just finished a 4ftx6ft Fruit basket block (on plywood) that her husband mounted on their barn. Looks great. We painted outdoor plywood (but not the marine treated kind) with primer and enamel, then put our pattern on using 2 to 3 coats of enamel for each color. It took about a week --was damp so drying between coats took a while.
We drew our pattern out "life size" and then transferred it to the wood. We just pencilled in the lines on the back side of our pattern and then laid it face up on the board and traced all the lines onto the board. It evolved a bit as we went along since our pattern was an original creation (just the pattern, not the idea).
There are a lot of these in eastern Kentucky as well as in Tenn. I think they originated in Iowa.
My sister's last name is "fruits" --hense the fruit basket block.