i use a cookie sheet that i got at a resturant supply , it was cheap like five dollars
This is the right answer for all drip pans, and for covering your bench when rebuilding transmissions or carbs, or taking apart anything that has a tends to dump fluids. Small sheets and pans are also really handy for keeping parts organized and keeping screws from rolling away.
The big commerical pans are the best and you can get them from the supply companies, or from an auction if you are lucky. Smaller pans can be found very cheaply at yard sales.
I have a dozen at home, and insisted on new ones from the restaurant supply store when we were speccing a new teardown bench at the new shop at work.