I made sure the projection is all consistent (although sometimes design / tile efficiency takes preference over that). I think what may be throwing it off for him is that the walls (under layer) are already 'sliced' quite low so that they take up exactly 1 tile without overlap. The roof tiles are not only just adding the roof, but also draw the rest of the wall that has been hidden. Had to do it like this for it to fit with other existing tiles (like the door frames).