Some islands can be bought undeveloped, while others already have roads and/or houses. Islands are also available for rent. Many celebrities have their own private islands. Commercial development of uninhabited islands can raise ecological concerns, as many have a fragile environment.

Private islands come in all shapes and sizes and can cost anywhere from $200,000 to $200 million, depending on what you're looking for. However, buying an island and building on it is a major investment of both time and money, so it's important to find the right one that's worth waiting for.

More than two years passed before he could get another commission but by then Krolow had 80 islands for sale, in different parts of the world. He also started buying islands himself. He and his company now own more than a dozen islands — in Canada, Panama, Belize and Fiji — which are rented out as holiday lets.

You can find private islands for sale via Private Islands Inc. or Vladi Private Islands, or by contacting a realtor who specializes in big-ticket sales. Additionally, some high-end real estate companies, like Sotheby's International Realty or Christie's International Real Estate, list private islands for sale.