Number 1:
You need to find out how many Muslims there are in your town.
Number 2:
Like the sis said, you need to approach the council, I dont know for you Americans it might be your mayoral office, I havent got a clue, and go to them, and talk to them. For all you know, they might even give you a place for free, if there are enough Muslims there...]
And Masha Allah, goon on ya for wanting to build a mosque..