Call me blind, but I've spent hour looking for the ceiling-turn tile like in 
under the animated door. Any suggestion where to look for it in 48x48 version?
I wasn't very specific, I wanted to do it with no wall, with a curve and no unnecessary line cuts:
But since it's just straight lines I managed to draw it myself, more or less. I have also drawn myself second version which has additional line separating bottom-going wall, like on the version you've made.