You can use any old text editor to make a PHP website - PHP scripting files are simply text files.
As far as "Real Estate" is concerned, being able to store photos/images and text against these images is more like a Content Management System (CMS). There are plenty of PHP-based CMS applications out there that can be used - just pick one that you can work with easily.
However, I would strongly suggest you get the client's requirements for the application before diving into the huge world of CMS building applications - it may be the case that any of the CMS out there will not be enough to cover all of the requirements. Real Estate may also involve sales (invoicing), market analysis, map plotting/GIS capabilities .... quite a lot for any single CMS out there!
Understand the business needs of the client first and, most importantly, plan. It would be an exciting project to manage and work on - good luck !!