This function will take a surface and then repeatedly tile it across the whole room, starting from the coordinates that you give in the function.
draw_surface_tiled(id, x, y);
|id||The unique ID value of the surface to draw.|
|x||The x position of where to draw the surface.|
|y||The y position of where to draw the surface.|
draw_surface_tiled(surf, x, y);
This will draw the surface indexed in "surf" at the instances own x and y position, and tiled in every direction in the room.