I've used Yakima rooftop racks on various vehicles since 2002 and have been very satisfied. I know you said you don't want to drill, but if you can't find a made to fit solution (as mentioned above for the 2dr) and you have to customize it, Yakima has a pretty good selection of landing pad bases, one of which should work. I have a flat roof on my pop-up camper so I used landing pad 6. The landing pads have 2 holes each, and as long as you measure twice, mark everything right,and center punch before drilling, it's not too scary
I've never had any leaks with the silicone sealer that is provided with the landing pad kits.
The real question would be, what's the roof structure like on the Corolla? if it's just flat sheet metal with little reinforcement, it may not be a good idea to use the landing pad option, or at least you'll want to put them as close to the edge as possible. Many of the made to fit solution mount out on the edge at the rain gutters where there is good structural support.
As also mentioned, gas mileage is affected to varying degrees. If I have something high or boxy on the racks on my toyota FJ, I've had as much as 3-4mpg drop. On the other hand I can put a roofbag with a more aerodynamic leading edge (angled/slanted) and not measure any difference at all. The rack on the camper, I don't notice aerodynamics at all cuz it's already a giant 4000+ lbs brick
