If you must put in on the roof, maybe concider wrapping in in a tarp first to cover it up. I believe it's not legal to transport a deer that way.

Another trick to hauling it INSIDE the truck costs a total of $12 at Walmart. I bought a children'splastic snowsled and a tarp. Iputthe deer in the sled and dragit out on the sled. The plasticslides easier than fur. I line the back of my SUV with a tarp and put the deer/sled in the back.The sled has 4-5inchhigh sides onit so most of the blood stays in the sled. The tarpis extra insurance. If it is warm weather, I put 2 bags of ice in the deer and the sled catches any water as the ice melts.