How much does it cost to build a gym?
Good answers. Your question is quite open-ended, as the responses indicate. As Michael suggests, a good first step is to develop a comprehensive business plan based on what type of facility you want to build and market. Who is your potential client base? What do anticipate your staffing needs to be? What kind of and how much equipment do want to have in the facility? Lots of important, specific questions you need to address completely as you put your business plan together.
Good luck.