I've found BinaryDriverHowto/AMD.
New items are in my comments ....
I have got amd-driver-installer-catalyst-15-20.1046-x86.x86_64.run in my Downloads folder ready to run, but when I'm trying to issue the command sh amd-driver-installer-catalyst-13-4-x86.x86_64.run --buildpkg Ubuntu/trusty, it does not want to run it. I have the error message:
sh: 0: Can't open amd-driver-installer-catalyst-15-20.1046-x86.x86_64.run
Can someone explain me what to do?