Here is a video that I created to show the different lines weights used in architectural drawing. My information comes from the book, Design Drawing, by Francis D. K. Ching with Steven P. Juroszek. You will discover more about this topic in the Pictorial Systems chapter. Mr. Ching is a master at explaining and visually demonstrating architectural drawing systems. I highly recommend that you take time to explore his books and visit his Seeing, Thinking, Drawing blog.