Type in "Car wash blueprints" in your search bar. You will find a number of resources that offer these plans right online. In most cases you will have to pay for these plans, but you might be lucky enough to find a few for free.
Search your local area for engineering companies that design commercial buildings. They will be located in business directories, in the yellow pages and online. Talk to a few of these companies and try to find out who draws blueprints for car washes. In some cases, they will sell you blueprints that they have already drawn or design new ones for you.
Contact the International Car Wash Association if you do not have any luck with engineering firms in your area. They may be able to give you advice on who to talk to. You can find them online at www.carwash.org.
Search your local library for books on the subject of opening a car wash. These books will help point you in the right direction. Your library may also have some blueprints in their engineering collection.
Visit your local university college of engineering or community technical college. They may have several car wash blueprints available to loan or for sale.