Welcome to Cabbage and Csound!
Do you want the pitch shifter to be before or after the reverb? I would recommend placing it before the reverb, that way the reverb will smear any artefacts introduced by the pitch shifter.
What way do you want to implement the pitch shifter? Using time domain processing (delays) or frequency domain processing (pvs opcodes)? I would recommend time domain in this context.
To implement the pitch shifter you could look at the example Examples/Effects/Spectral/PitchShifter.csd. It implements the time domain pitch shifter as a UDO so you should be able to transplant the code for the pitch shifter to your own project reasonably easily.
A rather nice thing you can do is to implement an FDN reverb and insert a pitch shifter within the global feedback loop. This creates an arpeggiating effect in which the pitch shifter interval is repeated over and over.
I hope this is of some help. If you need any clarification on any of this, please ask.