Whoa, wait a minute....
If I am reading this right, you are looking at adding a roof vent? Ok, no biggie, but understand, you are looking at "hood scoops" there. You mount a giant STI scoop (picture 1) and I can almost guarantee that your aero will be !@#$ed beyond comprehension. You need to look at the Spec C type vent for the WRX/STI. Way more low profile and made to function (if installed properly).
http://www.cardomain.com/ride/2396639
I seriously wouldn't put a hood scoop on my roof, especially as an engine air intake. In rally, they are for interior cooling/circulation, not engine related.