As far as "what's needed" -- same thing as with any house. You need to first talk to a lender to get prequalified for a mortgage (unless you're paying cash). The lender will look at debt to income ratio, credit score, job history, savings, etc. Once you find a house and put a contract on it, it's still the same process as buying new. You'll want to get it inspected, you'll need an appraisal, etc.