He colocado las sumas para que puedan guiarse facilmente.
<canvas width="600" height="400">
</canvas>
<script>
var pantalla = document.querySelector("canvas");
var pincel = pantalla.getContext("2d");
pincel.fillStyle = "lightgrey";
pincel.fillRect(0,0,600,400);
pincel.fillStyle = "darkgreen";
pincel.fillRect(125,50,350,300);
pincel.fillStyle = "black";
pincel.fillRect(175,110,90,90);
pincel.fillRect(175+70+90,110,90,90);
pincel.fillRect(175+90,110+90,70,100);
pincel.fillRect(175+50,110+90+40,40,110);
pincel.fillRect(175+90+70,110+40+90,40,110);
</script>
