This answer formalizes and expands on my earlier comment, because I don't like seeing unanswered questions and no one else has answered yet.
The Stack Exchange, as a whole, operates on a CC-BY-SA copyright model. As Tim mentions on this other question about the legality of re-using material found on the network, you should read the license to know what you can and cannot do (see the link in Tim's answer). However, in short, you can do whatever you want with the material from the site as long as say where you got the idea from and any changes you made to it.
That being said, the concept of a question requesting answers propose ideas for your world runs contrary to the purpose of the Worldbuilding SE. The community exists to provide solutions to problems you have, or to verify that what you have is consistent with the rest of your world. A question asking for the community to build parts of your world for you given an idea would probably be closed as either too broad or primarily opinion-based.
More accurately, this would fall under the idea generation close-reason we used to have, but got rid of because it was unclear for new users what it meant or how it applied.