Here is the steps you need to take:

Go into your applications folder and right or ctrl + click on Cubase 4. Select "show package contents". Go into the Contents folder then VST3 folder. Remove the file (may appear as a folder) 'Cubase Plug-in Set.vst3'. Then re-apply the 4.1 patch and Roomworks should appear and is now a VST3 plug-in.