First draw a line and then at the top of the line put a diagonal line and the same at the bottom.
Once you have done that add another diagonal line at the top.
After that join the top and bottom lines together and add a line at the top so that it looks like a square.
Add another line to the bottom left corner and join up the other points.
Now add some windows and doors.
At the top add some rectangles to make a ventilation system.