AS a quick note.
If you are making the upgrade to SCOM 1801 then there is a known issue with the Upgrade to the SSRS installation.
The work around for this is to install the SCOM console onto the SSRS instance first.
The key word in this sentence is FIRST.
If you run the upgrade without the console it will fail but just putting the console on and re-running the upgrade will not work.
This work around is known by the PG and they are working to remove the need for it in future CB releases of SCOM.