Sweet Home 3D 5.1
Sweet Home 3D 5.1 was released on October 5, 2015 with bug fixes and minor improvements described in version history.
I also checked Sweet Home 3D 5.1 works correctly under Mac OS X 10.11 (El Capitan) where you'll have to download Java 6 to run the installer version, or install Oracle Java version to launch the Java Web Start version. The good news are that Apple updated Mac OS X to let Java applications display elements of the user interface with the new look they updated a year ago.
Under Windows 10 released last summer, Sweet Home 3D works correctly too with a look matching system's one. A few users reported they had problems to run it under Windows 64 bit, but launching Java Web Start version with a 32 bit JRE seems to solve their problem. Let's hope future updates of Java and Windows will fix this issue.
Why the need of deprecated Java 6?
Don't let the marketing hype influence you: Apple Java 6 is very stable and have no problem of security in the case of applications. Binding Sweet Home 3D with Oracle Java 8 would prevent Mac OS X users to run Sweet Home 3D installer version under Mac OS X 10.4 to 10.6. Why excluding these users?
If you really want to run Sweet Home 3D with Java 8, use the Java Web Start version.