Most people scrape the roof and paint it with this while plastic like substance and repair any major ceiling cracks. Another way is to pour a second layer of concrete. Espect around 10-12k for a second layer and a little less 5-9 for the plastic paint repair
If you know what you doing is a heck of a lot cheaper. Either way, power wash it, fill cracks then use either option.
Many types of concrete, I have no clue which to use ask home depot and others. Also the amount of water versus concrete makes a big difference and getting the air bubbles out.
Also make sure you have good drainage so the water don't just sit there. All concrete roof will eventually leak, maintenance can extend it but eventually it will leak. Strong sun, heavy rains and the change in temperature eventually deteriorate it.
Tilted roof are in a way better for drainage but they tend to leak where they join the wall or the other section of the roof, not everyone is an expert at sealing it properly.
If you are serious about a particular house that has a leaky roof, get a contractor to go up there, take a look at the condition, measure it and give you a solid estimate, then you decide if it is worth it for you. If the contractor does not bring a ladder and climb up, get a new contractor, he is guessing. He also need to go inside the house and observer the damage inside.
