What Are The Most Common Issues / Challenges In Connecting Cameras On Different Floors?

Can someone advise me what the common issues are when connecting cameras on different floors. Let's say we have a residential building and we want to have cameras on the upper floors as well as the ground level. What should I look for? How hard/expensive can it get?

Try to find the existing cable/wire path that runs between the floors. Someone already drilled holes to run power wires, phone lines, cable TV wires between floors; they should have conduit running between the floors, hopefully one is open. Otherwise prepare to pay someone or rent a hammer drill large enough to drive a 1-2" hole through 18" of concrete.

The fact that you are asking says that it will be very difficult for you. Find a reliable electrician to help you.