As mentioned in the other post, we do really recommend using the automation tool to make a full ‘Rocket’ build for a reusable engine build. If it wasn’t clear you can do that by opening a command prompt in Engine/Build/BatchFiles and running:
RunUAT.bat GUBP -Node=GatherRocket -TargetPlatforms=Win32+Win64+... -NoDDC -CleanLocal
You may also need to add -NoSign if the machine building it is not capable of signing the build products. Once the command completes successfully you should find the build within the LocalBuilds folder of the UE4 root directory.
I see you’re working with the 4.12 preview, where we’ve changed the file used to indicate a pre-compiled engine build to InstalledBuild.txt to get rid of the Rocket terminology and make this a more generic use. Adding the InstalledBuild.txt file and the BaseEngine.ini entries is done after the engine has been built by GUBP and will prevent these from being built again so if you’re trying to set this up manually then they should definitely be done after building everything. Using the old Rocket.txt file was probably why it was still attempting to rebuild UnrealBuildTool. Hope that gets things working, let us know if not.