There's this artist called Viria who makes the oficial art of the Riordan universe. I absolutely love her style and the way she reflects the personality of our favourite characters is brilliant. Here are some of her drawings.
This is the last job I did for school. It consisted of drawing a cathedral taking care of the symmetry and using the ruler and the compass. The shadows haven't turned out particularly well for me, I think I'll have to work on that :)