Plot plans are typically created by a land surveyor, civil engineer, etc. to obtain a permit to improve property.
If you are searching for a previously prepared plot plan, you should contact the Department of Code Enforcement, Records Department to see if they have one on file. They can be found at 1200 Madison Avenue, Suite 100 (317) 327-3976
If they do not have one on file you might need to contact a private surveyor or civil engineer to draw one for you.