All of the information in the previous answers are true.
When purchasing a Co-op you are purchasing shares/stocks in the building, a proportionate interest. You will not receive a Deed but will receive a shares certificate, per se. Typically the monthly fees are higher and they include the real estate taxes for the unit. I currently have a co-op on the market in PA and have sold two others. This particular type of real estate is more prominent in New York and some other states so financing could also be a bit of a challenge. Most mortgage companies will shy away from giving a loan on co-ops or will charge extra high rates. You may do better going to a bank or savings and loan in the community where the co-op is located.
I hope this information helps.
Yes. As well, they are harder to resale. All prospects buyer have to be approved by the co-op's board of directors. There are many demands for personal-background and personal-finance information, comprehensive employment history and background checks.
It's also harder to sublease your co-op, and in many cases that is not allowed at all. Co-ops require larger down payments than condominiums, and all maintenance fees are higher than in condos, nevertheless they are tax-deductible.
Much will depend on the exact location, board requirements, size, condition, if looking to rent the unit check with managemrnt to see if it's allowed, etc.; do consider working with an agent of your own, he/she will be your best guide. Be aware that a mortgage pre-approval letter is required in order to determine your price range and for any offers to be taken seriously.