I started the shiplap on my fireplace wall. The wall is bowed in the middle (of course) so I had to add some 1/4″ trim to level out the boards.
And of course the ceiling isn’t level or plumb so I’ll be adding trim pieces at some point, but I did get the boards to line up pretty darn good!
I’m loving it so far. Hoping to work on the other wall soon . . . .