Hi! It looks like you've selected a single point of your roof and moved it forward slightly. Tiles are made of four points and two faces. To make it work, simply nudge the top point back into place by selecting it and moving it with the arrow keys.
To stretch the texture over your model, go into edit mode, select the tiles you want to change the texture on, and go to the tileset window. In the tileset window it'll show a pink/purple outline. You can drag the points of this outline to remap the texture.
Have you watched the video demonstration on making a house? It shows how to do this and a few other tips