Chandigarh flat: RERA concerns and builder delays

Kids have moved out, so we're selling our big house and looking for a smaller, manageable flat in New Chandigarh or Mohali. We're looking at projects by Godrej or Omaxe. How do you actually check RERA registration thoroughly? I mean, beyond just the number. What are the common red flags to look for when verifying a builder's legal track record before committing? Also, if a builder delays possession, what are our real legal options under RERA? Not sure if it's actually effective or just on paper. Any experiences or advice would be great.