I am designing the twelve levels of the game. It is a hard work to get them done. I try to make them really atmospheric and even depressive, while respecting the evolution of the game. Unity is the key!
I first use Tiled to make a tiled level and then I make a picture from it when the raw shape looks good. (I am actually here) From that picture I add non-tiled details and many other things. And then I should quickly assemble them in Construct 2 to try them. And certainly go back to the previous steps because everything wasn't perfect!