Construction of Simple NaI (Tl) detector

Hi.I am new to Geant4. after installation I have roamed around various examples of it.I have to make an NaI(Tl) detector for validation of gamma ray spectroscopy. Please suggest with which example should I proceed.I have very little knowledge of C++.I am learning to use gps but I dont know how to make data analysis in some examples where it is not already given like example B1. Please help!!!