have a look on autotiles, you should edit the parts to fit your game .
for this front wall you need three main parts, left , middle where no outlines on the left or the right, and right wall, then you need to make the left/right front walls connectable to side walls, for side walls you need top part, middle where no outlines in top/bottom and the bottom wall, now you have made a wall tileset that can connect and extended in a rect shape, now you need corners and inner walls that will make you able to design different shapes for each room.