That does what exactly? That is pretty open ended. Commercial or retail to start with. Selling properties or managing tenants? Lots of stuff on the market for real estate already not a market many FM people are in I think.
as is search for 'filemaker real estate' via google, bing, yahoo or your favorite search engine.
also sometimes when I need to set up a new client with a new solution, I might peruse the search engines for MySQL/PHP solutions. if they are open source, you can download and see what schema they have used. It is a good starting point to know what might be important. Many have "demo" versions to see what layouts/screens might be useful tor agents. I get lots of ideas that get me started in better directions that can be used with FileMaker.
p.s.I have created Real Estate solutions with MySQL/PHP for web.