[quote name='Ou7shined' timestamp='1391623961' post='2359406']
You may want to set a click track first though as it makes syncing everything much easier later on. This requires a MIDI track. Select your track (click on it) and with the right mouse drag/select say 4 bars, then at the top click Insert > New MIDI item. This creates a Midi zone in those 4 bars. Now click where it says FX on your track - this will open up all your plugins. You want a drum instrument so select VSTi in the left side. Now all your instrument plugins are listed. I think the only native plugin that you could create a metronome in is ReaSyndr - click on it. Now go back to your track and double click on the MIDI area. This will bring up your midi keyboard - you should be able to scroll through the various sounds. Simply click on whichever sound you want at the appropriate place in the bar (the grid) you wish it to make a sound.
Volume sliders on each track allow you to crudely "mix" the levels of each track.
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For a basic click track,
Reapers internal click is much easier - Just toggle it on and off, or use a key command - It is on the tool bar.
You can set it up for pre roll, x amount of bar(s) count in, and of course you can change the sound (.wav)
It will follow BPM changes.
http://en.wikiaudio.org/Reaper:Metronome
Of course, your way of doing it would be good for setting up off beats or odd time sig bars (3/8 etc) etc.
Maybe the latest update addresses this (I am not a Reaper user)