As everybody else seems to understand, he is asking what difference using extra-virgin olive oil in place of butter will make when making roux, other than the obvious difference in flavor. Seeing as everyone else understood this, this begs the question of just exactly who is in need of their sheepskin.
Two sayings apply here: 1. There are no stupid questions, only stupid answers, and 2. If you don't have anything nice to say, don't say anything at all.
On the topic, if you were making a dark roux, you might want to use an oil with a high smoke point to avoid any burnt flavor in your roux. Olive oil doesn't have as high a smoke point as other oils
. Also, as mentioned before, cooking destroys the flavor of the extra-virgin olive oil. A cheaper, neutral-flavored oil with a higher smoke point is your best bet.