Yo lo hice asi
<canvas width="600" height="400"> </canvas>
<script>
var pantalla = document.querySelector("canvas");
var pincel = pantalla.getContext("2d");
pincel.fillStyle = "darkgreen"
pincel.fillRect(75,20,350,300);
pincel.fillStyle = "black"
pincel.fillRect(120,70,90,90);
pincel.fillStyle = "black"
pincel.fillRect(280,70,90,90);
pincel.fillStyle = "black"
pincel.fillRect(210,160,70,100);
pincel.fillStyle = "black"
pincel.fillRect(280,210,40,110);
pincel.fillStyle = "black"
pincel.fillRect(170,210,40,110);
</script>
