There are a number of questions that should be asked before buying an airplane:
Buy versus Rent/Borrow - Through clubs or private organizations you can rent a plane on almost any given day. However, owning provides the pride of ownership, increased flexibility in flight times, and increased control over upkeep. Which choice makes the most sense for you?
Is It Affordable – The costs of buying an airplane include a down payment, principal and interest on a loan, insurance, storage, the annual inspection, regular maintenance, taxes, and fuel. How much can you afford?
Your Objective - Are you interested in acrobatics, sightseeing, fun flying, short trips, or cross-country trips? The best type and model depends on how you plan to use the plane.
Which Plane – Once you’ve decided on a model and a price range, how do you find, inspect and buy a used airplane?
http://www.ebuyingguides.com/how/uplaneb_h.htm