As an amateur wood worker, I'd suggest that you think of weather proof paint, and weather proofing the wood you use first of all.
I'd sand the wood first and put some sort of sealer on the ends all around it, then each time I put some on the front and back I'd add more to the ends, which wick up moisture faster than the flat wood does. Please don't ask how I learned this the hard way and ruined a good project.
First primer, remember that house paint is made just for weathering and would probably last a longer time than inside paints. Sand and fill any holes, like you were doing furniture or walls. If you want to be meticulous about it, then prime it again. My late DH was fussy as all get out, but his work lasted!!
Then you can start in with the marking and painting. But the first thing always is to weather proof it.
I just might make some smaller ones for our closed back yard garage, never thought to do something like that. It'll cheer up the yard in the dull winter time.