Here’s how I did a DIY statement wall for the bedroom of our youngest son. My wife wanted a cowboy theme, and wanted a bold wall. She chose the color and design of the molding.
I had to make sure to have the right width of molding (she didn’t want it too thin). I couldn’t find thick molding in long strips, so I had to piece together 36 inch slats of wood from Home Depot.

Measuring was the hardest part. Then I used liquid nails and small nails to tack it into place. Then I patched the seams with putty. After letting everything dry, I sanded the puttied seams. The last prep step was filling every edge with calking to make sure it was seamless.
At that point it was ready for primer, followed by the color. We got a flat finish, but paid a little extra for scuff protection, which was totally worth it.

The picture belonged to my grandparents and the bed was an online second-hand find for $30. The wood, paint, and other supplies cost about $200, so overall it was doable on a budget and we finished it in about 2-3 days total.