This is seriously mind bending!! Took me a while, but I was pleased to finish (and a nice twist in the last level - no spoilers). It felt really satisfying to work out myself what "adding shapes" means.
BTW, I probably found Washington Monument the hardest, as it was adding it in a way I wasn't expecting .. although I've just spotted it is one of your screenshots, so that would have been a helpful clue at the time!! :)
Well done