The back of our garage was covered with wood siding. I covered that with plywood, painted it and smoothed it with wood filler and a lot of sanding.
After the final coat of paint it rained heavily and some areas blistered. Oh, well, I went on with it anyways. At night I projected the drawing of my print "Eve" onto the finished wall and traced it with charcoal.
The fine details were hard to trace, so I decided to deal with them later.
That electric outlet in the middle of the drawing has to move.