If water is pouring through your ceiling during a heavy rain storm the problem is generally with either your roof or a blocked gutter.
Ice dams (water freezing and getting under the roof) during winter can cause water spotting and leaks once the ice starts to melt.
Snow can blow in through a ridge vent during a heavy snow storm. Once the snow melts it will cause water spots and leaks.
Water coming through a ceiling after a shower can be the result of a plumbing leak, but more frequently is the result of missing caulk—either in the tile or at the area where the tile meets the shower. Check the caulking carefully for open spaces and areas before calling a contractor.
If the tile work is bad and cannot be caulked, you may also want to replace the faucet (inside the wall) with a pressure balanced unit for safety before covering up the old faucet with expensive tile work. A plumbing contractor can provide you with assistance.