Usually building permit should be issued by city, not 小區開發商. Ple

make sure you got valid permit. You don't even need a builder's license to build a house. As long as your house meets local building code (city will inspect your work step by step. e.g. if you didn't pass fundation inspection, you can't start framing work). Like others said, you may want to talk to a lawyer to see if there's any special terms and conditions in your case as your land is inside of a developing 小區.