This calculator is designed to supply the area of any potential collection surface of any length and width in square feet and/or square inches, based on the length and width values entered in feet and inches, and the potential and estimated actual rainwater recovery in gallons.
It depends! Read the owner's manual for the brand of car you own or want to drive as each auto maker determines when to change the oil. Generally, I've read and experienced that full synthetic oil can last up to 5K-7500 miles, but... it also depends on other factors such as your driving style and where you live. VW has listed in its newer cars, like the 2015 VW Golf, that oil changes can be done in 10k miles!
That's not completely insane if you've had it on synthetic oil. Companies like Mobil 1 offer oils that are guaranteed up to 15,000 miles, and it's not unreasonable to see OEM's specify very long intervals (some VW's are 10,000, some Porsches are 15,000 mi). Provided you used decent oil, there shouldn't be any appreciable damage.